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 $41.35   6.604%   $44.0808   $44.08   $44.10   $44.10  
  Purchase #2 $202.51   4.486%   $211.5946   $211.59   $211.60   $211.60  
  Purchase #3 $26.26   6.286%   $27.9107   $27.91   $27.90   $27.90  
  Purchase #4 $102.62   7.243%   $110.0528   $110.05   $110.05   $110.10  
  Purchase #5 $153.57   10.120%   $169.1113   $169.11   $169.10   $169.10  
  Purchase #6 $240.80   8.683%   $261.7087   $261.71   $261.70   $261.70  
  Purchase #7 $181.92   5.200%   $191.3798   $191.38   $191.40   $191.40  
  7 purchase totals = $949.03       $1,015.8387   $1,015.83   $1,015.85   $1,015.90