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 $62.37   3.696%   $64.6752   $64.68   $64.70   $64.70  
  Purchase #2 $85.63   11.680%   $95.6316   $95.63   $95.65   $95.60  
  Purchase #3 $68.45   10.775%   $75.8255   $75.83   $75.85   $75.80  
  Purchase #4 $96.65   6.303%   $102.7418   $102.74   $102.75   $102.70  
  Purchase #5 $197.33   12.751%   $222.4915   $222.49   $222.50   $222.50  
  Purchase #6 $185.97   13.671%   $211.394   $211.39   $211.40   $211.40  
  Purchase #7 $212.30   11.195%   $236.067   $236.07   $236.05   $236.10  
  7 purchase totals = $908.70       $1,008.8266   $1,008.83   $1,008.90   $1,008.80