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 $46.79   13.245%   $52.9873   $52.99   $53.00   $53.00  
  Purchase #2 $136.65   7.585%   $147.0149   $147.01   $147.00   $147.00  
  Purchase #3 $166.57   8.378%   $180.5252   $180.53   $180.55   $180.50  
  Purchase #4 $72.38   11.343%   $80.5901   $80.59   $80.60   $80.60  
  Purchase #5 $246.87   11.658%   $275.6501   $275.65   $275.65   $275.70  
  Purchase #6 $104.90   6.727%   $111.9566   $111.96   $111.95   $112.00  
  Purchase #7 $99.69   6.545%   $106.2147   $106.21   $106.20   $106.20  
  7 purchase totals = $873.85       $954.9389   $954.94   $954.95   $955.00