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 $62.72   13.739%   $71.3371   $71.34   $71.35   $71.30  
  Purchase #2 $150.95   8.109%   $163.1905   $163.19   $163.20   $163.20  
  Purchase #3 $113.27   8.591%   $123.001   $123.00   $123.00   $123.00  
  Purchase #4 $208.32   3.236%   $215.0612   $215.06   $215.05   $215.10  
  Purchase #5 $205.97   5.279%   $216.8432   $216.84   $216.85   $216.80  
  Purchase #6 $44.26   11.179%   $49.2078   $49.21   $49.20   $49.20  
  Purchase #7 $202.30   8.182%   $218.8522   $218.85   $218.85   $218.90  
  7 purchase totals = $987.79       $1,057.4930   $1,057.49   $1,057.50   $1,057.50