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 $128.69   11.738%   $143.7956   $143.80   $143.80   $143.80  
  Purchase #2 $182.95   9.264%   $199.8985   $199.90   $199.90   $199.90  
  Purchase #3 $56.48   7.329%   $60.6194   $60.62   $60.60   $60.60  
  Purchase #4 $121.84   3.802%   $126.4724   $126.47   $126.45   $126.50  
  Purchase #5 $59.73   6.414%   $63.5611   $63.56   $63.55   $63.60  
  Purchase #6 $171.43   9.798%   $188.2267   $188.23   $188.25   $188.20  
  Purchase #7 $245.58   9.530%   $268.9838   $268.98   $269.00   $269.00  
  7 purchase totals = $966.70       $1,051.5575   $1,051.56   $1,051.55   $1,051.60