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 $84.59   10.284%   $93.2892   $93.29   $93.30   $93.30  
  Purchase #2 $211.85   11.425%   $236.0539   $236.05   $236.05   $236.10  
  Purchase #3 $102.77   8.232%   $111.23   $111.23   $111.25   $111.20  
  Purchase #4 $241.92   13.505%   $274.5913   $274.59   $274.60   $274.60  
  Purchase #5 $119.32   13.126%   $134.9819   $134.98   $135.00   $135.00  
  Purchase #6 $12.66   8.305%   $13.7114   $13.71   $13.70   $13.70  
  Purchase #7 $6.55   7.847%   $7.064   $7.06   $7.05   $7.10  
  7 purchase totals = $779.66       $870.9217   $870.91   $870.95   $871.00