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 $140.96   8.388%   $152.7837   $152.78   $152.80   $152.80  
  Purchase #2 $22.95   8.833%   $24.9772   $24.98   $25.00   $25.00  
  Purchase #3 $92.67   8.839%   $100.8611   $100.86   $100.85   $100.90  
  Purchase #4 $153.77   8.742%   $167.2126   $167.21   $167.20   $167.20  
  Purchase #5 $247.73   8.279%   $268.2396   $268.24   $268.25   $268.20  
  Purchase #6 $210.25   8.284%   $227.6671   $227.67   $227.65   $227.70  
  Purchase #7 $117.87   11.679%   $131.636   $131.64   $131.65   $131.60  
  7 purchase totals = $986.20       $1,073.3773   $1,073.38   $1,073.40   $1,073.40