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 $97.51   9.549%   $106.8212   $106.82   $106.80   $106.80  
  Purchase #2 $53.65   11.836%   $60   $60.00   $60.00   $60.00  
  Purchase #3 $100.83   5.117%   $105.9895   $105.99   $106.00   $106.00  
  Purchase #4 $231.72   13.580%   $263.1876   $263.19   $263.20   $263.20  
  Purchase #5 $130.53   5.610%   $137.8527   $137.85   $137.85   $137.90  
  Purchase #6 $46.94   5.577%   $49.5578   $49.56   $49.55   $49.60  
  Purchase #7 $203.85   10.693%   $225.6477   $225.65   $225.65   $225.60  
  7 purchase totals = $865.03       $949.0565   $949.06   $949.05   $949.10