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 $107.54   11.144%   $119.5243   $119.52   $119.50   $119.50  
  Purchase #2 $141.53   13.348%   $160.4214   $160.42   $160.40   $160.40  
  Purchase #3 $218.51   7.387%   $234.6513   $234.65   $234.65   $234.70  
  Purchase #4 $48.55   10.783%   $53.7851   $53.79   $53.80   $53.80  
  Purchase #5 $178.49   7.672%   $192.1838   $192.18   $192.20   $192.20  
  Purchase #6 $184.95   8.311%   $200.3212   $200.32   $200.30   $200.30  
  Purchase #7 $250.67   10.490%   $276.9653   $276.97   $276.95   $277.00  
  7 purchase totals = $1,130.24       $1,237.8524   $1,237.85   $1,237.80   $1,237.90