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 $20.58   9.328%   $22.4997   $22.50   $22.50   $22.50  
  Purchase #2 $105.60   4.497%   $110.3488   $110.35   $110.35   $110.30  
  Purchase #3 $5.46   6.148%   $5.7957   $5.80   $5.80   $5.80  
  Purchase #4 $207.96   7.401%   $223.3511   $223.35   $223.35   $223.40  
  Purchase #5 $146.88   12.295%   $164.9389   $164.94   $164.95   $164.90  
  Purchase #6 $91.62   9.761%   $100.563   $100.56   $100.55   $100.60  
  Purchase #7 $231.44   6.748%   $247.0576   $247.06   $247.05   $247.10  
  7 purchase totals = $809.54       $874.5548   $874.56   $874.55   $874.60