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 $26.52   3.248%   $27.3814   $27.38   $27.40   $27.40  
  Purchase #2 $231.60   3.473%   $239.6435   $239.64   $239.65   $239.60  
  Purchase #3 $126.48   12.367%   $142.1218   $142.12   $142.10   $142.10  
  Purchase #4 $206.95   6.675%   $220.7639   $220.76   $220.75   $220.80  
  Purchase #5 $85.32   3.358%   $88.185   $88.19   $88.20   $88.20  
  Purchase #6 $47.96   4.373%   $50.0573   $50.06   $50.05   $50.10  
  Purchase #7 $218.64   12.457%   $245.876   $245.88   $245.90   $245.90  
  7 purchase totals = $943.47       $1,014.0289   $1,014.03   $1,014.05   $1,014.10