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 $67.35   12.285%   $75.6239   $75.62   $75.60   $75.60  
  Purchase #2 $180.80   12.168%   $202.7997   $202.80   $202.80   $202.80  
  Purchase #3 $78.79   7.738%   $84.8868   $84.89   $84.90   $84.90  
  Purchase #4 $54.31   7.157%   $58.197   $58.20   $58.20   $58.20  
  Purchase #5 $230.70   11.266%   $256.6907   $256.69   $256.70   $256.70  
  Purchase #6 $175.99   10.594%   $194.6344   $194.63   $194.65   $194.60  
  Purchase #7 $228.52   12.133%   $256.2463   $256.25   $256.25   $256.20  
  7 purchase totals = $1,016.46       $1,129.0788   $1,129.08   $1,129.10   $1,129.00