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 $205.67   4.136%   $214.1765   $214.18   $214.20   $214.20  
  Purchase #2 $29.46   7.592%   $31.6966   $31.70   $31.70   $31.70  
  Purchase #3 $113.67   13.320%   $128.8108   $128.81   $128.80   $128.80  
  Purchase #4 $111.30   7.605%   $119.7644   $119.76   $119.75   $119.80  
  Purchase #5 $191.48   5.324%   $201.6744   $201.67   $201.65   $201.70  
  Purchase #6 $5.63   10.256%   $6.2074   $6.21   $6.20   $6.20  
  Purchase #7 $52.28   5.790%   $55.307   $55.31   $55.30   $55.30  
  7 purchase totals = $709.49       $757.6371   $757.64   $757.60   $757.70