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 $248.77   7.635%   $267.7636   $267.76   $267.75   $267.80  
  Purchase #2 $189.53   11.168%   $210.6967   $210.70   $210.70   $210.70  
  Purchase #3 $178.63   6.397%   $190.057   $190.06   $190.05   $190.10  
  Purchase #4 $236.36   11.653%   $263.903   $263.90   $263.90   $263.90  
  Purchase #5 $192.32   12.414%   $216.1946   $216.19   $216.20   $216.20  
  Purchase #6 $120.53   7.741%   $129.8602   $129.86   $129.85   $129.90  
  Purchase #7 $145.87   6.744%   $155.7075   $155.71   $155.70   $155.70  
  7 purchase totals = $1,312.01       $1,434.1826   $1,434.18   $1,434.15   $1,434.30