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 $117.90   6.169%   $125.1733   $125.17   $125.15   $125.20  
  Purchase #2 $83.51   9.642%   $91.562   $91.56   $91.55   $91.60  
  Purchase #3 $58.68   13.588%   $66.6534   $66.65   $66.65   $66.70  
  Purchase #4 $227.34   5.457%   $239.7459   $239.75   $239.75   $239.70  
  Purchase #5 $231.66   5.295%   $243.9264   $243.93   $243.95   $243.90  
  Purchase #6 $96.90   12.620%   $109.1288   $109.13   $109.15   $109.10  
  Purchase #7 $216.34   7.442%   $232.44   $232.44   $232.45   $232.40  
  7 purchase totals = $1,032.33       $1,108.6298   $1,108.63   $1,108.65   $1,108.60