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 $27.48   12.864%   $31.015   $31.02   $31.00   $31.00  
  Purchase #2 $133.58   10.541%   $147.6607   $147.66   $147.65   $147.70  
  Purchase #3 $162.97   9.446%   $178.3641   $178.36   $178.35   $178.40  
  Purchase #4 $237.73   11.788%   $265.7536   $265.75   $265.75   $265.80  
  Purchase #5 $186.99   3.426%   $193.3963   $193.40   $193.40   $193.40  
  Purchase #6 $185.44   7.319%   $199.0124   $199.01   $199.00   $199.00  
  Purchase #7 $55.66   12.185%   $62.4422   $62.44   $62.45   $62.40  
  7 purchase totals = $989.85       $1,077.6443   $1,077.64   $1,077.60   $1,077.70