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 $239.58   11.778%   $267.7977   $267.80   $267.80   $267.80  
  Purchase #2 $153.95   7.761%   $165.8981   $165.90   $165.90   $165.90  
  Purchase #3 $73.65   11.231%   $81.9216   $81.92   $81.90   $81.90  
  Purchase #4 $136.60   11.205%   $151.906   $151.91   $151.90   $151.90  
  Purchase #5 $230.42   10.344%   $254.2546   $254.25   $254.25   $254.30  
  Purchase #6 $187.98   9.740%   $206.2893   $206.29   $206.30   $206.30  
  Purchase #7 $110.27   5.783%   $116.6469   $116.65   $116.65   $116.60  
  7 purchase totals = $1,132.45       $1,244.7142   $1,244.72   $1,244.70   $1,244.70