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 $107.82   13.621%   $122.5062   $122.51   $122.50   $122.50  
  Purchase #2 $124.53   13.283%   $141.0713   $141.07   $141.05   $141.10  
  Purchase #3 $183.74   8.184%   $198.7773   $198.78   $198.80   $198.80  
  Purchase #4 $47.38   6.204%   $50.3195   $50.32   $50.30   $50.30  
  Purchase #5 $84.50   3.574%   $87.52   $87.52   $87.50   $87.50  
  Purchase #6 $40.98   13.647%   $46.5725   $46.57   $46.55   $46.60  
  Purchase #7 $171.58   4.616%   $179.5001   $179.50   $179.50   $179.50  
  7 purchase totals = $760.53       $826.2669   $826.27   $826.20   $826.30