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 $56.44   6.321%   $60.0076   $60.01   $60.00   $60.00  
  Purchase #2 $153.98   8.582%   $167.1946   $167.19   $167.20   $167.20  
  Purchase #3 $249.83   3.677%   $259.0162   $259.02   $259.00   $259.00  
  Purchase #4 $93.35   7.470%   $100.3232   $100.32   $100.30   $100.30  
  Purchase #5 $70.63   5.731%   $74.6778   $74.68   $74.70   $74.70  
  Purchase #6 $151.52   12.516%   $170.4842   $170.48   $170.50   $170.50  
  Purchase #7 $215.84   4.276%   $225.0693   $225.07   $225.05   $225.10  
  7 purchase totals = $991.59       $1,056.7729   $1,056.77   $1,056.75   $1,056.80