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 $243.99   8.625%   $265.0341   $265.03   $265.05   $265.00  
  Purchase #2 $203.93   7.214%   $218.6415   $218.64   $218.65   $218.60  
  Purchase #3 $149.99   9.177%   $163.7546   $163.75   $163.75   $163.80  
  Purchase #4 $220.98   10.512%   $244.2094   $244.21   $244.20   $244.20  
  Purchase #5 $213.98   9.295%   $233.8694   $233.87   $233.85   $233.90  
  Purchase #6 $211.61   8.624%   $229.8592   $229.86   $229.85   $229.90  
  Purchase #7 $238.29   8.331%   $258.1419   $258.14   $258.15   $258.10  
  7 purchase totals = $1,482.77       $1,613.5101   $1,613.50   $1,613.50   $1,613.50