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 $41.37   8.684%   $44.9626   $44.96   $44.95   $45.00  
  Purchase #2 $120.39   11.281%   $133.9712   $133.97   $133.95   $134.00  
  Purchase #3 $32.88   12.746%   $37.0709   $37.07   $37.05   $37.10  
  Purchase #4 $212.40   8.296%   $230.0207   $230.02   $230.00   $230.00  
  Purchase #5 $36.91   7.412%   $39.6458   $39.65   $39.65   $39.60  
  Purchase #6 $215.43   8.259%   $233.2224   $233.22   $233.20   $233.20  
  Purchase #7 $65.76   11.690%   $73.4473   $73.45   $73.45   $73.40  
  7 purchase totals = $725.14       $792.3409   $792.34   $792.25   $792.30