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 $25.28   6.850%   $27.0117   $27.01   $27.00   $27.00  
  Purchase #2 $175.89   11.333%   $195.8236   $195.82   $195.80   $195.80  
  Purchase #3 $174.72   13.354%   $198.0521   $198.05   $198.05   $198.10  
  Purchase #4 $119.66   10.717%   $132.484   $132.48   $132.50   $132.50  
  Purchase #5 $202.86   9.348%   $221.8234   $221.82   $221.80   $221.80  
  Purchase #6 $162.68   3.507%   $168.3852   $168.39   $168.40   $168.40  
  Purchase #7 $62.79   12.779%   $70.8139   $70.81   $70.80   $70.80  
  7 purchase totals = $923.88       $1,014.3939   $1,014.38   $1,014.35   $1,014.40