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 $131.87   10.744%   $146.0381   $146.04   $146.05   $146.00  
  Purchase #2 $100.67   9.826%   $110.5618   $110.56   $110.55   $110.60  
  Purchase #3 $153.87   12.751%   $173.49   $173.49   $173.50   $173.50  
  Purchase #4 $168.71   3.704%   $174.959   $174.96   $174.95   $175.00  
  Purchase #5 $207.81   6.446%   $221.2054   $221.21   $221.20   $221.20  
  Purchase #6 $64.43   11.514%   $71.8485   $71.85   $71.85   $71.80  
  Purchase #7 $169.88   12.255%   $190.6988   $190.70   $190.70   $190.70  
  7 purchase totals = $997.24       $1,088.8016   $1,088.81   $1,088.80   $1,088.80