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 $243.95   8.859%   $265.5615   $265.56   $265.55   $265.60  
  Purchase #2 $33.75   3.581%   $34.9586   $34.96   $34.95   $35.00  
  Purchase #3 $240.94   10.468%   $266.1616   $266.16   $266.15   $266.20  
  Purchase #4 $72.28   12.802%   $81.5333   $81.53   $81.55   $81.50  
  Purchase #5 $99.98   10.204%   $110.182   $110.18   $110.20   $110.20  
  Purchase #6 $152.81   7.662%   $164.5183   $164.52   $164.50   $164.50  
  Purchase #7 $131.55   7.435%   $141.3307   $141.33   $141.35   $141.30  
  7 purchase totals = $975.26       $1,064.2460   $1,064.24   $1,064.25   $1,064.30