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 $194.54   10.176%   $214.3364   $214.34   $214.35   $214.30  
  Purchase #2 $241.96   7.223%   $259.4368   $259.44   $259.45   $259.40  
  Purchase #3 $98.91   10.123%   $108.9227   $108.92   $108.90   $108.90  
  Purchase #4 $104.67   8.221%   $113.2749   $113.27   $113.25   $113.30  
  Purchase #5 $37.76   6.499%   $40.214   $40.21   $40.20   $40.20  
  Purchase #6 $186.78   4.406%   $195.0095   $195.01   $195.00   $195.00  
  Purchase #7 $84.56   4.455%   $88.3271   $88.33   $88.35   $88.30  
  7 purchase totals = $949.18       $1,019.5214   $1,019.52   $1,019.50   $1,019.40