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 $93.35   10.692%   $103.331   $103.33   $103.35   $103.30  
  Purchase #2 $110.58   6.316%   $117.5642   $117.56   $117.55   $117.60  
  Purchase #3 $56.60   13.113%   $64.022   $64.02   $64.00   $64.00  
  Purchase #4 $248.74   4.764%   $260.59   $260.59   $260.60   $260.60  
  Purchase #5 $87.82   7.218%   $94.1588   $94.16   $94.15   $94.20  
  Purchase #6 $105.47   6.585%   $112.4152   $112.42   $112.40   $112.40  
  Purchase #7 $19.54   8.414%   $21.1841   $21.18   $21.20   $21.20  
  7 purchase totals = $722.10       $773.2653   $773.26   $773.25   $773.30