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 $39.41   13.106%   $44.5751   $44.58   $44.60   $44.60  
  Purchase #2 $91.98   8.308%   $99.6217   $99.62   $99.60   $99.60  
  Purchase #3 $160.43   4.202%   $167.1713   $167.17   $167.15   $167.20  
  Purchase #4 $213.85   7.385%   $229.6428   $229.64   $229.65   $229.60  
  Purchase #5 $150.97   4.380%   $157.5825   $157.58   $157.60   $157.60  
  Purchase #6 $136.41   9.754%   $149.7154   $149.72   $149.70   $149.70  
  Purchase #7 $142.47   13.702%   $161.9912   $161.99   $162.00   $162.00  
  7 purchase totals = $935.52       $1,010.3000   $1,010.30   $1,010.30   $1,010.30