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 $136.29   13.484%   $154.6673   $154.67   $154.65   $154.70  
  Purchase #2 $161.87   11.695%   $180.8007   $180.80   $180.80   $180.80  
  Purchase #3 $8.88   4.494%   $9.2791   $9.28   $9.30   $9.30  
  Purchase #4 $249.43   6.479%   $265.5906   $265.59   $265.60   $265.60  
  Purchase #5 $131.75   5.861%   $139.4719   $139.47   $139.45   $139.50  
  Purchase #6 $69.36   5.196%   $72.9639   $72.96   $72.95   $73.00  
  Purchase #7 $188.75   11.797%   $211.0168   $211.02   $211.00   $211.00  
  7 purchase totals = $946.33       $1,033.7903   $1,033.79   $1,033.75   $1,033.90