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 $148.64   5.565%   $156.9118   $156.91   $156.90   $156.90  
  Purchase #2 $58.65   13.390%   $66.5032   $66.50   $66.50   $66.50  
  Purchase #3 $174.43   12.343%   $195.9599   $195.96   $195.95   $196.00  
  Purchase #4 $230.54   4.224%   $240.278   $240.28   $240.30   $240.30  
  Purchase #5 $173.59   6.674%   $185.1754   $185.18   $185.20   $185.20  
  Purchase #6 $120.33   10.575%   $133.0549   $133.05   $133.05   $133.10  
  Purchase #7 $88.93   6.164%   $94.4116   $94.41   $94.40   $94.40  
  7 purchase totals = $995.11       $1,072.2948   $1,072.29   $1,072.30   $1,072.40