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 $29.57   12.548%   $33.2804   $33.28   $33.30   $33.30  
  Purchase #2 $130.98   3.352%   $135.3704   $135.37   $135.35   $135.40  
  Purchase #3 $56.46   9.854%   $62.0236   $62.02   $62.00   $62.00  
  Purchase #4 $246.37   8.549%   $267.4322   $267.43   $267.45   $267.40  
  Purchase #5 $33.50   12.748%   $37.7706   $37.77   $37.75   $37.80  
  Purchase #6 $239.59   6.479%   $255.113   $255.11   $255.10   $255.10  
  Purchase #7 $170.73   9.475%   $186.9067   $186.91   $186.90   $186.90  
  7 purchase totals = $907.20       $977.8969   $977.89   $977.85   $977.90