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 $60.69   7.203%   $65.0615   $65.06   $65.05   $65.10  
  Purchase #2 $127.78   8.281%   $138.3615   $138.36   $138.35   $138.40  
  Purchase #3 $153.27   7.127%   $164.1936   $164.19   $164.20   $164.20  
  Purchase #4 $207.26   10.836%   $229.7187   $229.72   $229.70   $229.70  
  Purchase #5 $210.78   13.365%   $238.9507   $238.95   $238.95   $239.00  
  Purchase #6 $86.51   11.292%   $96.2787   $96.28   $96.30   $96.30  
  Purchase #7 $245.65   9.325%   $268.5569   $268.56   $268.55   $268.60  
  7 purchase totals = $1,091.94       $1,201.1216   $1,201.12   $1,201.10   $1,201.30