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 $80.47   9.357%   $87.9996   $88.00   $88.00   $88.00  
  Purchase #2 $218.96   11.704%   $244.5871   $244.59   $244.60   $244.60  
  Purchase #3 $85.84   8.293%   $92.9587   $92.96   $92.95   $93.00  
  Purchase #4 $186.84   8.783%   $203.2502   $203.25   $203.25   $203.30  
  Purchase #5 $156.36   7.871%   $168.6671   $168.67   $168.65   $168.70  
  Purchase #6 $119.92   12.537%   $134.9544   $134.95   $134.95   $135.00  
  Purchase #7 $39.56   3.172%   $40.8148   $40.81   $40.80   $40.80  
  7 purchase totals = $887.95       $973.2319   $973.23   $973.20   $973.40