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 $125.57   12.805%   $141.6492   $141.65   $141.65   $141.60  
  Purchase #2 $19.30   12.212%   $21.6569   $21.66   $21.65   $21.70  
  Purchase #3 $47.58   9.257%   $51.9845   $51.98   $52.00   $52.00  
  Purchase #4 $194.43   7.653%   $209.3097   $209.31   $209.30   $209.30  
  Purchase #5 $49.41   7.273%   $53.0036   $53.00   $53.00   $53.00  
  Purchase #6 $175.65   7.621%   $189.0363   $189.04   $189.05   $189.00  
  Purchase #7 $124.87   7.813%   $134.6261   $134.63   $134.65   $134.60  
  7 purchase totals = $736.81       $801.2663   $801.27   $801.30   $801.20