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 $192.82   10.437%   $212.9446   $212.94   $212.95   $212.90  
  Purchase #2 $24.25   4.559%   $25.3556   $25.36   $25.35   $25.40  
  Purchase #3 $235.37   4.501%   $245.964   $245.96   $245.95   $246.00  
  Purchase #4 $201.88   7.550%   $217.1219   $217.12   $217.10   $217.10  
  Purchase #5 $136.73   5.393%   $144.1038   $144.10   $144.10   $144.10  
  Purchase #6 $143.97   5.593%   $152.0222   $152.02   $152.00   $152.00  
  Purchase #7 $33.94   7.173%   $36.3745   $36.37   $36.35   $36.40  
  7 purchase totals = $968.96       $1,033.8866   $1,033.87   $1,033.80   $1,033.90