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 $48.98   5.568%   $51.7072   $51.71   $51.70   $51.70  
  Purchase #2 $64.93   3.675%   $67.3162   $67.32   $67.30   $67.30  
  Purchase #3 $163.51   7.249%   $175.3628   $175.36   $175.35   $175.40  
  Purchase #4 $203.83   5.432%   $214.902   $214.90   $214.90   $214.90  
  Purchase #5 $73.77   6.347%   $78.4522   $78.45   $78.45   $78.50  
  Purchase #6 $10.55   7.723%   $11.3648   $11.36   $11.35   $11.40  
  Purchase #7 $190.30   6.368%   $202.4183   $202.42   $202.40   $202.40  
  7 purchase totals = $755.87       $801.5235   $801.52   $801.45   $801.60