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 $45.48   10.334%   $50.1799   $50.18   $50.20   $50.20  
  Purchase #2 $233.83   11.739%   $261.2793   $261.28   $261.30   $261.30  
  Purchase #3 $54.77   12.114%   $61.4048   $61.40   $61.40   $61.40  
  Purchase #4 $150.43   10.855%   $166.7592   $166.76   $166.75   $166.80  
  Purchase #5 $182.98   7.660%   $196.9963   $197.00   $197.00   $197.00  
  Purchase #6 $184.90   9.140%   $201.7999   $201.80   $201.80   $201.80  
  Purchase #7 $108.67   11.847%   $121.5441   $121.54   $121.55   $121.50  
  7 purchase totals = $961.06       $1,059.9635   $1,059.96   $1,060.00   $1,060.00