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 $54.73   7.810%   $59.0044   $59.00   $59.00   $59.00  
  Purchase #2 $186.86   10.670%   $206.798   $206.80   $206.80   $206.80  
  Purchase #3 $211.97   12.295%   $238.0317   $238.03   $238.05   $238.00  
  Purchase #4 $191.62   5.444%   $202.0518   $202.05   $202.05   $202.10  
  Purchase #5 $47.41   6.722%   $50.5969   $50.60   $50.60   $50.60  
  Purchase #6 $160.26   8.830%   $174.411   $174.41   $174.40   $174.40  
  Purchase #7 $90.51   5.795%   $95.7551   $95.76   $95.75   $95.80  
  7 purchase totals = $943.36       $1,026.6489   $1,026.65   $1,026.65   $1,026.70