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 $223.97   9.655%   $245.5943   $245.59   $245.60   $245.60  
  Purchase #2 $246.86   10.285%   $272.2496   $272.25   $272.25   $272.20  
  Purchase #3 $39.49   9.279%   $43.1543   $43.15   $43.15   $43.20  
  Purchase #4 $182.75   6.364%   $194.3802   $194.38   $194.40   $194.40  
  Purchase #5 $118.96   5.846%   $125.9144   $125.91   $125.90   $125.90  
  Purchase #6 $124.36   5.492%   $131.1899   $131.19   $131.20   $131.20  
  Purchase #7 $41.85   13.811%   $47.6299   $47.63   $47.65   $47.60  
  7 purchase totals = $978.24       $1,060.1126   $1,060.10   $1,060.15   $1,060.10