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 $205.48   9.681%   $225.3725   $225.37   $225.35   $225.40  
  Purchase #2 $136.71   13.467%   $155.1207   $155.12   $155.10   $155.10  
  Purchase #3 $126.38   12.327%   $141.9589   $141.96   $141.95   $142.00  
  Purchase #4 $206.57   9.395%   $225.9773   $225.98   $226.00   $226.00  
  Purchase #5 $223.43   13.324%   $253.1998   $253.20   $253.20   $253.20  
  Purchase #6 $246.96   3.483%   $255.5616   $255.56   $255.55   $255.60  
  Purchase #7 $61.93   9.390%   $67.7452   $67.75   $67.75   $67.70  
  7 purchase totals = $1,207.46       $1,324.9360   $1,324.94   $1,324.90   $1,325.00