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 $153.47   10.129%   $169.015   $169.02   $169.00   $169.00  
  Purchase #2 $96.72   6.799%   $103.296   $103.30   $103.30   $103.30  
  Purchase #3 $134.69   9.201%   $147.0828   $147.08   $147.10   $147.10  
  Purchase #4 $151.68   11.812%   $169.5964   $169.60   $169.60   $169.60  
  Purchase #5 $170.75   13.747%   $194.223   $194.22   $194.20   $194.20  
  Purchase #6 $105.34   5.607%   $111.2464   $111.25   $111.25   $111.20  
  Purchase #7 $70.74   7.578%   $76.1007   $76.10   $76.10   $76.10  
  7 purchase totals = $883.39       $970.5603   $970.57   $970.55   $970.50