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 $38.54   13.513%   $43.7479   $43.75   $43.75   $43.70  
  Purchase #2 $78.53   4.437%   $82.0144   $82.01   $82.00   $82.00  
  Purchase #3 $155.33   3.153%   $160.2276   $160.23   $160.25   $160.20  
  Purchase #4 $122.79   12.795%   $138.501   $138.50   $138.50   $138.50  
  Purchase #5 $161.52   11.104%   $179.4552   $179.46   $179.45   $179.50  
  Purchase #6 $150.87   12.454%   $169.6593   $169.66   $169.65   $169.70  
  Purchase #7 $247.38   13.853%   $281.6496   $281.65   $281.65   $281.60  
  7 purchase totals = $954.96       $1,055.2550   $1,055.26   $1,055.25   $1,055.20