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 $245.75   11.164%   $273.1855   $273.19   $273.20   $273.20  
  Purchase #2 $16.44   7.133%   $17.6127   $17.61   $17.60   $17.60  
  Purchase #3 $184.74   7.335%   $198.2907   $198.29   $198.30   $198.30  
  Purchase #4 $88.49   3.384%   $91.4845   $91.48   $91.50   $91.50  
  Purchase #5 $137.90   12.410%   $155.0134   $155.01   $155.00   $155.00  
  Purchase #6 $113.65   5.801%   $120.2428   $120.24   $120.25   $120.20  
  Purchase #7 $169.66   10.675%   $187.7712   $187.77   $187.75   $187.80  
  7 purchase totals = $956.63       $1,043.6008   $1,043.59   $1,043.60   $1,043.60