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 $233.97   7.631%   $251.8243   $251.82   $251.80   $251.80  
  Purchase #2 $204.79   3.321%   $211.5911   $211.59   $211.60   $211.60  
  Purchase #3 $64.42   6.625%   $68.6878   $68.69   $68.70   $68.70  
  Purchase #4 $82.56   6.179%   $87.6614   $87.66   $87.65   $87.70  
  Purchase #5 $164.98   6.196%   $175.2022   $175.20   $175.20   $175.20  
  Purchase #6 $10.30   8.429%   $11.1682   $11.17   $11.15   $11.20  
  Purchase #7 $232.63   11.678%   $259.7965   $259.80   $259.80   $259.80  
  7 purchase totals = $993.65       $1,065.9315   $1,065.93   $1,065.90   $1,066.00