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 $66.29   5.609%   $70.0082   $70.01   $70.00   $70.00  
  Purchase #2 $103.76   8.749%   $112.838   $112.84   $112.85   $112.80  
  Purchase #3 $94.49   9.796%   $103.7462   $103.75   $103.75   $103.70  
  Purchase #4 $240.59   5.741%   $254.4023   $254.40   $254.40   $254.40  
  Purchase #5 $247.89   8.179%   $268.1649   $268.16   $268.15   $268.20  
  Purchase #6 $138.35   5.669%   $146.1931   $146.19   $146.20   $146.20  
  Purchase #7 $100.75   4.460%   $105.2435   $105.24   $105.25   $105.20  
  7 purchase totals = $992.12       $1,060.5962   $1,060.59   $1,060.60   $1,060.50