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 $44.57   13.157%   $50.4341   $50.43   $50.45   $50.40  
  Purchase #2 $171.87   8.479%   $186.4429   $186.44   $186.45   $186.40  
  Purchase #3 $79.53   7.476%   $85.4757   $85.48   $85.50   $85.50  
  Purchase #4 $216.37   10.844%   $239.8332   $239.83   $239.85   $239.80  
  Purchase #5 $141.94   5.471%   $149.7055   $149.71   $149.70   $149.70  
  Purchase #6 $154.90   4.808%   $162.3476   $162.35   $162.35   $162.30  
  Purchase #7 $150.71   12.402%   $169.4011   $169.40   $169.40   $169.40  
  7 purchase totals = $959.89       $1,043.6401   $1,043.64   $1,043.70   $1,043.50