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 $74.41   12.533%   $83.7358   $83.74   $83.75   $83.70  
  Purchase #2 $136.75   6.255%   $145.3037   $145.30   $145.30   $145.30  
  Purchase #3 $116.26   6.120%   $123.3751   $123.38   $123.40   $123.40  
  Purchase #4 $210.63   13.716%   $239.52   $239.52   $239.50   $239.50  
  Purchase #5 $164.51   5.438%   $173.4561   $173.46   $173.45   $173.50  
  Purchase #6 $171.25   9.648%   $187.7722   $187.77   $187.75   $187.80  
  Purchase #7 $101.79   13.800%   $115.837   $115.84   $115.85   $115.80  
  7 purchase totals = $975.60       $1,068.9999   $1,069.01   $1,069.00   $1,069.00