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 $168.34   13.574%   $191.1905   $191.19   $191.20   $191.20  
  Purchase #2 $180.76   6.567%   $192.6305   $192.63   $192.65   $192.60  
  Purchase #3 $217.79   12.344%   $244.674   $244.67   $244.65   $244.70  
  Purchase #4 $134.99   4.264%   $140.746   $140.75   $140.75   $140.70  
  Purchase #5 $221.99   6.653%   $236.759   $236.76   $236.75   $236.80  
  Purchase #6 $182.72   11.116%   $203.0312   $203.03   $203.05   $203.00  
  Purchase #7 $225.96   9.689%   $247.8533   $247.85   $247.85   $247.90  
  7 purchase totals = $1,332.55       $1,456.8845   $1,456.88   $1,456.90   $1,456.90