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 $26.52   3.819%   $27.5328   $27.53   $27.55   $27.50  
  Purchase #2 $118.99   11.580%   $132.769   $132.77   $132.75   $132.80  
  Purchase #3 $38.79   5.704%   $41.0026   $41.00   $41.00   $41.00  
  Purchase #4 $31.48   3.833%   $32.6866   $32.69   $32.70   $32.70  
  Purchase #5 $224.64   3.110%   $231.6263   $231.63   $231.65   $231.60  
  Purchase #6 $85.93   13.222%   $97.2917   $97.29   $97.30   $97.30  
  Purchase #7 $187.27   7.335%   $201.0063   $201.01   $201.00   $201.00  
  7 purchase totals = $713.62       $763.9153   $763.92   $763.95   $763.90