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 $201.61   12.247%   $226.3012   $226.30   $226.30   $226.30  
  Purchase #2 $209.87   6.711%   $223.9544   $223.95   $223.95   $224.00  
  Purchase #3 $54.77   5.322%   $57.6849   $57.68   $57.70   $57.70  
  Purchase #4 $109.49   6.674%   $116.7974   $116.80   $116.80   $116.80  
  Purchase #5 $96.79   8.168%   $104.6958   $104.70   $104.70   $104.70  
  Purchase #6 $86.29   7.658%   $92.8981   $92.90   $92.90   $92.90  
  Purchase #7 $242.35   7.473%   $260.4608   $260.46   $260.45   $260.50  
  7 purchase totals = $1,001.17       $1,082.7926   $1,082.79   $1,082.80   $1,082.90