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 $246.47   8.566%   $267.5826   $267.58   $267.60   $267.60  
  Purchase #2 $135.73   10.165%   $149.527   $149.53   $149.55   $149.50  
  Purchase #3 $105.64   7.692%   $113.7658   $113.77   $113.75   $113.80  
  Purchase #4 $213.87   7.743%   $230.43   $230.43   $230.45   $230.40  
  Purchase #5 $82.78   6.561%   $88.2112   $88.21   $88.20   $88.20  
  Purchase #6 $27.95   6.468%   $29.7578   $29.76   $29.75   $29.80  
  Purchase #7 $91.82   3.761%   $95.2734   $95.27   $95.25   $95.30  
  7 purchase totals = $904.26       $974.5478   $974.55   $974.55   $974.60