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 $136.94   3.195%   $141.3152   $141.32   $141.30   $141.30  
  Purchase #2 $80.83   8.722%   $87.88   $87.88   $87.90   $87.90  
  Purchase #3 $41.98   9.450%   $45.9471   $45.95   $45.95   $45.90  
  Purchase #4 $245.82   13.667%   $279.4162   $279.42   $279.40   $279.40  
  Purchase #5 $245.27   9.266%   $267.9967   $268.00   $268.00   $268.00  
  Purchase #6 $62.97   12.696%   $70.9647   $70.96   $70.95   $71.00  
  Purchase #7 $200.75   12.800%   $226.446   $226.45   $226.45   $226.40  
  7 purchase totals = $1,014.56       $1,119.9659   $1,119.98   $1,119.95   $1,119.90