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 $92.39   6.557%   $98.448   $98.45   $98.45   $98.40  
  Purchase #2 $111.98   8.348%   $121.3281   $121.33   $121.35   $121.30  
  Purchase #3 $61.31   6.381%   $65.2222   $65.22   $65.20   $65.20  
  Purchase #4 $239.29   6.234%   $254.2073   $254.21   $254.20   $254.20  
  Purchase #5 $11.37   9.485%   $12.4484   $12.45   $12.45   $12.40  
  Purchase #6 $241.89   10.521%   $267.3392   $267.34   $267.35   $267.30  
  Purchase #7 $199.62   7.187%   $213.9667   $213.97   $213.95   $214.00  
  7 purchase totals = $957.85       $1,032.9599   $1,032.97   $1,032.95   $1,032.80