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 $48.57   5.718%   $51.3472   $51.35   $51.35   $51.30  
  Purchase #2 $68.53   13.194%   $77.5718   $77.57   $77.55   $77.60  
  Purchase #3 $169.60   10.333%   $187.1248   $187.12   $187.10   $187.10  
  Purchase #4 $235.59   10.380%   $260.0442   $260.04   $260.05   $260.00  
  Purchase #5 $88.55   6.333%   $94.1579   $94.16   $94.15   $94.20  
  Purchase #6 $176.52   5.715%   $186.6081   $186.61   $186.60   $186.60  
  Purchase #7 $167.85   11.481%   $187.1209   $187.12   $187.10   $187.10  
  7 purchase totals = $955.21       $1,043.9749   $1,043.97   $1,043.90   $1,043.90