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 $52.91   12.716%   $59.638   $59.64   $59.65   $59.60  
  Purchase #2 $150.62   13.258%   $170.5892   $170.59   $170.60   $170.60  
  Purchase #3 $186.94   9.304%   $204.3329   $204.33   $204.35   $204.30  
  Purchase #4 $163.36   12.733%   $184.1606   $184.16   $184.15   $184.20  
  Purchase #5 $127.95   5.594%   $135.1075   $135.11   $135.10   $135.10  
  Purchase #6 $106.54   4.704%   $111.5516   $111.55   $111.55   $111.60  
  Purchase #7 $119.73   9.184%   $130.726   $130.73   $130.75   $130.70  
  7 purchase totals = $908.05       $996.1058   $996.11   $996.15   $996.10