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 $114.88   3.341%   $118.7181   $118.72   $118.70   $118.70  
  Purchase #2 $106.73   12.284%   $119.8407   $119.84   $119.85   $119.80  
  Purchase #3 $167.97   13.313%   $190.3318   $190.33   $190.35   $190.30  
  Purchase #4 $124.64   4.429%   $130.1603   $130.16   $130.15   $130.20  
  Purchase #5 $212.80   5.564%   $224.6402   $224.64   $224.65   $224.60  
  Purchase #6 $100.45   4.413%   $104.8829   $104.88   $104.90   $104.90  
  Purchase #7 $30.85   7.751%   $33.2412   $33.24   $33.25   $33.20  
  7 purchase totals = $858.32       $921.8152   $921.81   $921.85   $921.70