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 $102.63   9.538%   $112.4188   $112.42   $112.40   $112.40  
  Purchase #2 $98.39   3.153%   $101.4922   $101.49   $101.50   $101.50  
  Purchase #3 $20.69   6.642%   $22.0642   $22.06   $22.05   $22.10  
  Purchase #4 $20.39   7.803%   $21.981   $21.98   $22.00   $22.00  
  Purchase #5 $87.44   4.109%   $91.0329   $91.03   $91.05   $91.00  
  Purchase #6 $73.88   8.434%   $80.111   $80.11   $80.10   $80.10  
  Purchase #7 $181.54   10.750%   $201.0556   $201.06   $201.05   $201.10  
  7 purchase totals = $584.96       $630.1557   $630.15   $630.15   $630.20