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 $146.93   13.670%   $167.0153   $167.02   $167.00   $167.00  
  Purchase #2 $200.73   12.468%   $225.757   $225.76   $225.75   $225.80  
  Purchase #3 $222.67   12.726%   $251.007   $251.01   $251.00   $251.00  
  Purchase #4 $5.64   10.374%   $6.2251   $6.23   $6.25   $6.20  
  Purchase #5 $197.52   10.527%   $218.3129   $218.31   $218.30   $218.30  
  Purchase #6 $40.64   9.664%   $44.5674   $44.57   $44.55   $44.60  
  Purchase #7 $72.36   4.641%   $75.7182   $75.72   $75.70   $75.70  
  7 purchase totals = $886.49       $988.6029   $988.62   $988.55   $988.60