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 $243.91   10.476%   $269.462   $269.46   $269.45   $269.50  
  Purchase #2 $38.64   6.634%   $41.2034   $41.20   $41.20   $41.20  
  Purchase #3 $84.52   4.185%   $88.0572   $88.06   $88.05   $88.10  
  Purchase #4 $88.84   6.174%   $94.325   $94.33   $94.35   $94.30  
  Purchase #5 $178.95   6.171%   $189.993   $189.99   $190.00   $190.00  
  Purchase #6 $185.87   7.436%   $199.6913   $199.69   $199.70   $199.70  
  Purchase #7 $72.62   3.741%   $75.3367   $75.34   $75.35   $75.30  
  7 purchase totals = $893.35       $958.0686   $958.07   $958.10   $958.10