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 $58.61   6.515%   $62.4284   $62.43   $62.45   $62.40  
  Purchase #2 $63.57   13.558%   $72.1888   $72.19   $72.20   $72.20  
  Purchase #3 $65.59   5.215%   $69.0105   $69.01   $69.00   $69.00  
  Purchase #4 $202.65   13.126%   $229.2498   $229.25   $229.25   $229.20  
  Purchase #5 $54.31   10.470%   $59.9963   $60.00   $60.00   $60.00  
  Purchase #6 $78.54   5.265%   $82.6751   $82.68   $82.70   $82.70  
  Purchase #7 $214.78   12.641%   $241.9303   $241.93   $241.95   $241.90  
  7 purchase totals = $738.05       $817.4792   $817.49   $817.55   $817.40