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 $248.34   11.507%   $276.9165   $276.92   $276.90   $276.90  
  Purchase #2 $89.95   8.627%   $97.71   $97.71   $97.70   $97.70  
  Purchase #3 $11.34   5.220%   $11.9319   $11.93   $11.95   $11.90  
  Purchase #4 $214.56   4.378%   $223.9534   $223.95   $223.95   $224.00  
  Purchase #5 $202.78   12.833%   $228.8028   $228.80   $228.80   $228.80  
  Purchase #6 $125.82   8.745%   $136.823   $136.82   $136.80   $136.80  
  Purchase #7 $180.53   12.701%   $203.4591   $203.46   $203.45   $203.50  
  7 purchase totals = $1,073.32       $1,179.5967   $1,179.59   $1,179.55   $1,179.60