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 $54.46   12.316%   $61.1673   $61.17   $61.15   $61.20  
  Purchase #2 $209.67   9.527%   $229.6453   $229.65   $229.65   $229.60  
  Purchase #3 $118.31   12.553%   $133.1615   $133.16   $133.15   $133.20  
  Purchase #4 $138.39   13.377%   $156.9024   $156.90   $156.90   $156.90  
  Purchase #5 $68.81   11.289%   $76.578   $76.58   $76.60   $76.60  
  Purchase #6 $129.52   13.717%   $147.2863   $147.29   $147.30   $147.30  
  Purchase #7 $201.81   7.847%   $217.646   $217.65   $217.65   $217.60  
  7 purchase totals = $920.97       $1,022.3868   $1,022.40   $1,022.40   $1,022.40