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 $66.56   13.469%   $75.525   $75.53   $75.55   $75.50  
  Purchase #2 $232.26   4.715%   $243.2111   $243.21   $243.20   $243.20  
  Purchase #3 $55.66   7.617%   $59.8996   $59.90   $59.90   $59.90  
  Purchase #4 $51.81   3.384%   $53.5633   $53.56   $53.55   $53.60  
  Purchase #5 $212.44   9.228%   $232.044   $232.04   $232.05   $232.00  
  Purchase #6 $183.38   8.208%   $198.4318   $198.43   $198.45   $198.40  
  Purchase #7 $192.88   9.167%   $210.5613   $210.56   $210.55   $210.60  
  7 purchase totals = $994.99       $1,073.2361   $1,073.23   $1,073.25   $1,073.20