Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $116.94   5.308%   $123.1472   $123.15   $123.15   $123.10  
  Purchase #2 $160.51   13.305%   $181.8659   $181.87   $181.85   $181.90  
  Purchase #3 $235.42   4.823%   $246.7743   $246.77   $246.75   $246.80  
  Purchase #4 $240.87   10.188%   $265.4098   $265.41   $265.40   $265.40  
  Purchase #5 $128.82   4.527%   $134.6517   $134.65   $134.65   $134.70  
  Purchase #6 $243.91   9.376%   $266.779   $266.78   $266.80   $266.80  
  Purchase #7 $220.81   11.407%   $245.9978   $246.00   $246.00   $246.00  
  7 purchase totals = $1,347.28       $1,464.6257   $1,464.63   $1,464.60   $1,464.70