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 $206.97   12.610%   $233.0689   $233.07   $233.05   $233.10  
  Purchase #2 $16.46   11.327%   $18.3244   $18.32   $18.30   $18.30  
  Purchase #3 $151.97   4.690%   $159.0974   $159.10   $159.10   $159.10  
  Purchase #4 $201.96   4.743%   $211.539   $211.54   $211.55   $211.50  
  Purchase #5 $14.39   5.686%   $15.2082   $15.21   $15.20   $15.20  
  Purchase #6 $240.87   11.451%   $268.452   $268.45   $268.45   $268.50  
  Purchase #7 $220.88   11.521%   $246.3276   $246.33   $246.35   $246.30  
  7 purchase totals = $1,053.50       $1,152.0175   $1,152.02   $1,152.00   $1,152.00