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 $24.60   8.771%   $26.7577   $26.76   $26.75   $26.80  
  Purchase #2 $51.59   4.610%   $53.9683   $53.97   $53.95   $54.00  
  Purchase #3 $133.95   4.728%   $140.2832   $140.28   $140.30   $140.30  
  Purchase #4 $234.55   7.680%   $252.5634   $252.56   $252.55   $252.60  
  Purchase #5 $170.67   11.122%   $189.6519   $189.65   $189.65   $189.70  
  Purchase #6 $12.49   5.546%   $13.1827   $13.18   $13.20   $13.20  
  Purchase #7 $68.74   5.637%   $72.6149   $72.61   $72.60   $72.60  
  7 purchase totals = $696.59       $749.0221   $749.01   $749.00   $749.20