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 $67.88   12.112%   $76.1016   $76.10   $76.10   $76.10  
  Purchase #2 $172.93   5.746%   $182.8666   $182.87   $182.85   $182.90  
  Purchase #3 $202.80   12.753%   $228.6631   $228.66   $228.65   $228.70  
  Purchase #4 $49.29   12.812%   $55.605   $55.61   $55.60   $55.60  
  Purchase #5 $120.78   12.316%   $135.6553   $135.66   $135.65   $135.70  
  Purchase #6 $207.92   4.683%   $217.6569   $217.66   $217.65   $217.70  
  Purchase #7 $26.29   5.496%   $27.7349   $27.73   $27.75   $27.70  
  7 purchase totals = $847.89       $924.2834   $924.29   $924.25   $924.40