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 $66.95   11.574%   $74.6988   $74.70   $74.70   $74.70  
  Purchase #2 $75.33   8.873%   $82.014   $82.01   $82.00   $82.00  
  Purchase #3 $26.60   3.616%   $27.5619   $27.56   $27.55   $27.60  
  Purchase #4 $169.61   10.646%   $187.6667   $187.67   $187.65   $187.70  
  Purchase #5 $199.49   4.357%   $208.1818   $208.18   $208.20   $208.20  
  Purchase #6 $23.94   10.416%   $26.4336   $26.43   $26.45   $26.40  
  Purchase #7 $247.46   6.278%   $262.9955   $263.00   $263.00   $263.00  
  7 purchase totals = $809.38       $869.5523   $869.55   $869.55   $869.60