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 $36.59   13.817%   $41.6456   $41.65   $41.65   $41.60  
  Purchase #2 $198.83   11.401%   $221.4986   $221.50   $221.50   $221.50  
  Purchase #3 $8.68   6.863%   $9.2757   $9.28   $9.30   $9.30  
  Purchase #4 $52.30   12.360%   $58.7643   $58.76   $58.75   $58.80  
  Purchase #5 $90.55   3.425%   $93.6513   $93.65   $93.65   $93.70  
  Purchase #6 $247.97   13.746%   $282.056   $282.06   $282.05   $282.10  
  Purchase #7 $72.56   8.220%   $78.5244   $78.52   $78.50   $78.50  
  7 purchase totals = $707.48       $785.4159   $785.42   $785.40   $785.50