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 $200.52   6.230%   $213.0124   $213.01   $213.00   $213.00  
  Purchase #2 $154.57   8.664%   $167.9619   $167.96   $167.95   $168.00  
  Purchase #3 $46.32   5.151%   $48.7059   $48.71   $48.70   $48.70  
  Purchase #4 $211.92   5.791%   $224.1923   $224.19   $224.20   $224.20  
  Purchase #5 $196.71   3.310%   $203.2211   $203.22   $203.20   $203.20  
  Purchase #6 $14.30   8.257%   $15.4808   $15.48   $15.50   $15.50  
  Purchase #7 $132.68   6.471%   $141.2657   $141.27   $141.25   $141.30  
  7 purchase totals = $957.02       $1,013.8401   $1,013.84   $1,013.80   $1,013.90