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 $55.37   11.562%   $61.7719   $61.77   $61.75   $61.80  
  Purchase #2 $120.48   12.856%   $135.9689   $135.97   $135.95   $136.00  
  Purchase #3 $64.72   13.497%   $73.4553   $73.46   $73.45   $73.50  
  Purchase #4 $132.91   3.781%   $137.9353   $137.94   $137.95   $137.90  
  Purchase #5 $179.89   6.605%   $191.7717   $191.77   $191.75   $191.80  
  Purchase #6 $55.51   6.202%   $58.9527   $58.95   $58.95   $59.00  
  Purchase #7 $204.96   3.236%   $211.5925   $211.59   $211.60   $211.60  
  7 purchase totals = $813.84       $871.4483   $871.45   $871.40   $871.60