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 $22.69   6.832%   $24.2402   $24.24   $24.25   $24.20  
  Purchase #2 $84.63   13.532%   $96.0821   $96.08   $96.10   $96.10  
  Purchase #3 $124.96   13.757%   $142.1507   $142.15   $142.15   $142.20  
  Purchase #4 $59.95   11.799%   $67.0235   $67.02   $67.00   $67.00  
  Purchase #5 $148.94   3.452%   $154.0814   $154.08   $154.10   $154.10  
  Purchase #6 $81.95   11.748%   $91.5775   $91.58   $91.60   $91.60  
  Purchase #7 $199.36   12.621%   $224.5212   $224.52   $224.50   $224.50  
  7 purchase totals = $722.48       $799.6766   $799.67   $799.70   $799.70