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 $59.80   6.719%   $63.818   $63.82   $63.80   $63.80  
  Purchase #2 $232.63   9.588%   $254.9346   $254.93   $254.95   $254.90  
  Purchase #3 $39.97   3.106%   $41.2115   $41.21   $41.20   $41.20  
  Purchase #4 $171.97   4.309%   $179.3802   $179.38   $179.40   $179.40  
  Purchase #5 $47.42   7.180%   $50.8248   $50.82   $50.80   $50.80  
  Purchase #6 $186.87   10.706%   $206.8763   $206.88   $206.90   $206.90  
  Purchase #7 $211.48   6.873%   $226.015   $226.02   $226.00   $226.00  
  7 purchase totals = $950.14       $1,023.0604   $1,023.06   $1,023.05   $1,023.00