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 $10.65   10.146%   $11.7305   $11.73   $11.75   $11.70  
  Purchase #2 $17.79   13.830%   $20.2504   $20.25   $20.25   $20.30  
  Purchase #3 $57.67   9.145%   $62.9439   $62.94   $62.95   $62.90  
  Purchase #4 $208.69   5.148%   $219.4334   $219.43   $219.45   $219.40  
  Purchase #5 $69.83   4.575%   $73.0247   $73.02   $73.00   $73.00  
  Purchase #6 $237.46   13.220%   $268.8522   $268.85   $268.85   $268.90  
  Purchase #7 $160.28   4.715%   $167.8372   $167.84   $167.85   $167.80  
  7 purchase totals = $762.37       $824.0723   $824.06   $824.10   $824.00