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 $238.87   12.157%   $267.9094   $267.91   $267.90   $267.90  
  Purchase #2 $112.89   3.687%   $117.0523   $117.05   $117.05   $117.10  
  Purchase #3 $93.35   11.523%   $104.1067   $104.11   $104.10   $104.10  
  Purchase #4 $153.62   9.746%   $168.5918   $168.59   $168.60   $168.60  
  Purchase #5 $206.70   8.236%   $223.7238   $223.72   $223.70   $223.70  
  Purchase #6 $226.49   6.227%   $240.5935   $240.59   $240.60   $240.60  
  Purchase #7 $100.34   9.753%   $110.1262   $110.13   $110.15   $110.10  
  7 purchase totals = $1,132.26       $1,232.1037   $1,232.10   $1,232.10   $1,232.10