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 $86.55   5.224%   $91.0714   $91.07   $91.05   $91.10  
  Purchase #2 $37.65   11.769%   $42.081   $42.08   $42.10   $42.10  
  Purchase #3 $152.95   12.739%   $172.4343   $172.43   $172.45   $172.40  
  Purchase #4 $175.42   7.223%   $188.0906   $188.09   $188.10   $188.10  
  Purchase #5 $11.80   10.791%   $13.0733   $13.07   $13.05   $13.10  
  Purchase #6 $140.61   6.276%   $149.4347   $149.43   $149.45   $149.40  
  Purchase #7 $135.45   8.836%   $147.4184   $147.42   $147.40   $147.40  
  7 purchase totals = $740.43       $803.6037   $803.59   $803.60   $803.60