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 $239.83   12.403%   $269.5761   $269.58   $269.60   $269.60  
  Purchase #2 $153.69   5.152%   $161.6081   $161.61   $161.60   $161.60  
  Purchase #3 $156.25   5.290%   $164.5156   $164.52   $164.50   $164.50  
  Purchase #4 $122.61   5.320%   $129.1329   $129.13   $129.15   $129.10  
  Purchase #5 $158.42   12.319%   $177.9358   $177.94   $177.95   $177.90  
  Purchase #6 $81.58   5.363%   $85.9551   $85.96   $85.95   $86.00  
  Purchase #7 $31.52   4.262%   $32.8634   $32.86   $32.85   $32.90  
  7 purchase totals = $943.90       $1,021.5870   $1,021.60   $1,021.60   $1,021.60