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 $181.81   12.313%   $204.1963   $204.20   $204.20   $204.20  
  Purchase #2 $105.98   6.637%   $113.0139   $113.01   $113.00   $113.00  
  Purchase #3 $236.63   8.683%   $257.1766   $257.18   $257.20   $257.20  
  Purchase #4 $7.41   6.713%   $7.9074   $7.91   $7.90   $7.90  
  Purchase #5 $25.85   12.666%   $29.1242   $29.12   $29.10   $29.10  
  Purchase #6 $242.80   6.657%   $258.9632   $258.96   $258.95   $259.00  
  Purchase #7 $81.51   4.373%   $85.0744   $85.07   $85.05   $85.10  
  7 purchase totals = $881.99       $955.4560   $955.45   $955.40   $955.50