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 $48.99   4.282%   $51.0878   $51.09   $51.10   $51.10  
  Purchase #2 $209.85   11.742%   $234.4906   $234.49   $234.50   $234.50  
  Purchase #3 $164.93   13.588%   $187.3407   $187.34   $187.35   $187.30  
  Purchase #4 $124.45   8.646%   $135.2099   $135.21   $135.20   $135.20  
  Purchase #5 $220.25   12.650%   $248.1116   $248.11   $248.10   $248.10  
  Purchase #6 $77.40   6.293%   $82.2708   $82.27   $82.25   $82.30  
  Purchase #7 $142.57   9.749%   $156.4691   $156.47   $156.45   $156.50  
  7 purchase totals = $988.44       $1,094.9805   $1,094.98   $1,094.95   $1,095.00