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 $184.93   8.671%   $200.9653   $200.97   $200.95   $201.00  
  Purchase #2 $77.89   7.496%   $83.7286   $83.73   $83.75   $83.70  
  Purchase #3 $118.73   7.338%   $127.4424   $127.44   $127.45   $127.40  
  Purchase #4 $189.51   10.164%   $208.7718   $208.77   $208.75   $208.80  
  Purchase #5 $161.77   13.538%   $183.6704   $183.67   $183.65   $183.70  
  Purchase #6 $207.36   13.845%   $236.069   $236.07   $236.05   $236.10  
  Purchase #7 $72.49   11.604%   $80.9017   $80.90   $80.90   $80.90  
  7 purchase totals = $1,012.68       $1,121.5492   $1,121.55   $1,121.50   $1,121.60