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 $235.41   13.864%   $268.0472   $268.05   $268.05   $268.00  
  Purchase #2 $228.63   10.505%   $252.6476   $252.65   $252.65   $252.60  
  Purchase #3 $164.89   3.814%   $171.1789   $171.18   $171.20   $171.20  
  Purchase #4 $148.45   11.442%   $165.4356   $165.44   $165.45   $165.40  
  Purchase #5 $184.87   7.203%   $198.1862   $198.19   $198.20   $198.20  
  Purchase #6 $62.45   3.819%   $64.835   $64.84   $64.85   $64.80  
  Purchase #7 $229.63   11.515%   $256.0719   $256.07   $256.05   $256.10  
  7 purchase totals = $1,254.33       $1,376.4024   $1,376.42   $1,376.45   $1,376.30