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 $120.48   13.669%   $136.9484   $136.95   $136.95   $136.90  
  Purchase #2 $174.39   5.313%   $183.6553   $183.66   $183.65   $183.70  
  Purchase #3 $59.39   12.733%   $66.9521   $66.95   $66.95   $67.00  
  Purchase #4 $45.48   12.771%   $51.2883   $51.29   $51.30   $51.30  
  Purchase #5 $161.85   9.331%   $176.9522   $176.95   $176.95   $177.00  
  Purchase #6 $235.62   12.588%   $265.2798   $265.28   $265.30   $265.30  
  Purchase #7 $233.26   12.798%   $263.1126   $263.11   $263.10   $263.10  
  7 purchase totals = $1,030.47       $1,144.1887   $1,144.19   $1,144.20   $1,144.30