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 $96.93   11.235%   $107.8201   $107.82   $107.80   $107.80  
  Purchase #2 $69.73   3.173%   $71.9425   $71.94   $71.95   $71.90  
  Purchase #3 $177.77   7.213%   $190.5926   $190.59   $190.60   $190.60  
  Purchase #4 $114.34   4.262%   $119.2132   $119.21   $119.20   $119.20  
  Purchase #5 $34.68   9.118%   $37.8421   $37.84   $37.85   $37.80  
  Purchase #6 $238.71   12.471%   $268.4795   $268.48   $268.50   $268.50  
  Purchase #7 $181.53   11.151%   $201.7724   $201.77   $201.75   $201.80  
  7 purchase totals = $913.69       $997.6624   $997.65   $997.65   $997.60