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 $63.59   5.869%   $67.3221   $67.32   $67.30   $67.30  
  Purchase #2 $188.78   3.620%   $195.6138   $195.61   $195.60   $195.60  
  Purchase #3 $103.91   12.294%   $116.6847   $116.68   $116.70   $116.70  
  Purchase #4 $12.61   11.304%   $14.0354   $14.04   $14.05   $14.00  
  Purchase #5 $193.78   13.484%   $219.9093   $219.91   $219.90   $219.90  
  Purchase #6 $159.63   7.713%   $171.9423   $171.94   $171.95   $171.90  
  Purchase #7 $82.91   9.800%   $91.0352   $91.04   $91.05   $91.00  
  7 purchase totals = $805.21       $876.5428   $876.54   $876.55   $876.40