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 $207.44   13.596%   $235.6435   $235.64   $235.65   $235.60  
  Purchase #2 $211.56   12.593%   $238.2018   $238.20   $238.20   $238.20  
  Purchase #3 $118.35   10.313%   $130.5554   $130.56   $130.55   $130.60  
  Purchase #4 $70.95   6.599%   $75.632   $75.63   $75.65   $75.60  
  Purchase #5 $223.79   6.563%   $238.4773   $238.48   $238.50   $238.50  
  Purchase #6 $202.39   11.505%   $225.675   $225.68   $225.70   $225.70  
  Purchase #7 $108.46   3.281%   $112.0186   $112.02   $112.00   $112.00  
  7 purchase totals = $1,142.94       $1,256.2036   $1,256.21   $1,256.25   $1,256.20