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 $241.64   6.582%   $257.5447   $257.54   $257.55   $257.50  
  Purchase #2 $202.63   11.624%   $226.1837   $226.18   $226.20   $226.20  
  Purchase #3 $215.58   11.385%   $240.1238   $240.12   $240.10   $240.10  
  Purchase #4 $217.92   4.704%   $228.171   $228.17   $228.15   $228.20  
  Purchase #5 $207.85   5.220%   $218.6998   $218.70   $218.70   $218.70  
  Purchase #6 $82.90   4.111%   $86.308   $86.31   $86.30   $86.30  
  Purchase #7 $225.38   8.654%   $244.8844   $244.88   $244.90   $244.90  
  7 purchase totals = $1,393.90       $1,501.9154   $1,501.90   $1,501.90   $1,501.90