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 $61.89   11.227%   $68.8384   $68.84   $68.85   $68.80  
  Purchase #2 $245.79   8.814%   $267.4539   $267.45   $267.45   $267.50  
  Purchase #3 $71.45   6.368%   $75.9999   $76.00   $76.00   $76.00  
  Purchase #4 $238.90   3.299%   $246.7813   $246.78   $246.80   $246.80  
  Purchase #5 $178.28   3.640%   $184.7694   $184.77   $184.75   $184.80  
  Purchase #6 $97.82   12.459%   $110.0074   $110.01   $110.00   $110.00  
  Purchase #7 $187.69   6.112%   $199.1616   $199.16   $199.15   $199.20  
  7 purchase totals = $1,081.82       $1,153.0119   $1,153.01   $1,153.00   $1,153.10