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 $147.46   10.753%   $163.3164   $163.32   $163.30   $163.30  
  Purchase #2 $126.66   6.151%   $134.4509   $134.45   $134.45   $134.50  
  Purchase #3 $229.72   5.729%   $242.8807   $242.88   $242.90   $242.90  
  Purchase #4 $216.78   4.368%   $226.249   $226.25   $226.25   $226.20  
  Purchase #5 $22.85   9.683%   $25.0626   $25.06   $25.05   $25.10  
  Purchase #6 $92.65   10.229%   $102.1272   $102.13   $102.15   $102.10  
  Purchase #7 $119.42   10.352%   $131.7824   $131.78   $131.80   $131.80  
  7 purchase totals = $955.54       $1,025.8692   $1,025.87   $1,025.90   $1,025.90