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 $70.59   5.833%   $74.7075   $74.71   $74.70   $74.70  
  Purchase #2 $226.25   3.260%   $233.6258   $233.63   $233.65   $233.60  
  Purchase #3 $147.42   13.274%   $166.9885   $166.99   $167.00   $167.00  
  Purchase #4 $191.87   6.708%   $204.7406   $204.74   $204.75   $204.70  
  Purchase #5 $43.51   11.164%   $48.3675   $48.37   $48.35   $48.40  
  Purchase #6 $211.72   11.269%   $235.5787   $235.58   $235.60   $235.60  
  Purchase #7 $183.27   9.758%   $201.1535   $201.15   $201.15   $201.20  
  7 purchase totals = $1,074.63       $1,165.1621   $1,165.17   $1,165.20   $1,165.20