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 $67.93   11.202%   $75.5395   $75.54   $75.55   $75.50  
  Purchase #2 $217.38   13.444%   $246.6046   $246.60   $246.60   $246.60  
  Purchase #3 $173.54   11.602%   $193.6741   $193.67   $193.65   $193.70  
  Purchase #4 $133.69   13.481%   $151.7127   $151.71   $151.70   $151.70  
  Purchase #5 $156.76   12.817%   $176.8519   $176.85   $176.85   $176.90  
  Purchase #6 $217.56   3.323%   $224.7895   $224.79   $224.80   $224.80  
  Purchase #7 $24.25   11.827%   $27.118   $27.12   $27.10   $27.10  
  7 purchase totals = $991.11       $1,096.2903   $1,096.28   $1,096.25   $1,096.30