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 $112.94   10.841%   $125.1838   $125.18   $125.20   $125.20  
  Purchase #2 $111.91   4.234%   $116.6483   $116.65   $116.65   $116.60  
  Purchase #3 $52.65   5.850%   $55.73   $55.73   $55.75   $55.70  
  Purchase #4 $215.92   11.718%   $241.2215   $241.22   $241.20   $241.20  
  Purchase #5 $175.51   6.505%   $186.9269   $186.93   $186.95   $186.90  
  Purchase #6 $234.38   12.217%   $263.0142   $263.01   $263.00   $263.00  
  Purchase #7 $95.51   6.445%   $101.6656   $101.67   $101.65   $101.70  
  7 purchase totals = $998.82       $1,090.3903   $1,090.39   $1,090.40   $1,090.30