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 $73.85   13.232%   $83.6218   $83.62   $83.60   $83.60  
  Purchase #2 $143.34   9.656%   $157.1809   $157.18   $157.20   $157.20  
  Purchase #3 $85.31   12.183%   $95.7033   $95.70   $95.70   $95.70  
  Purchase #4 $187.68   12.423%   $210.9955   $211.00   $211.00   $211.00  
  Purchase #5 $37.46   9.717%   $41.1   $41.10   $41.10   $41.10  
  Purchase #6 $33.74   6.582%   $35.9608   $35.96   $35.95   $36.00  
  Purchase #7 $223.61   5.637%   $236.2149   $236.21   $236.20   $236.20  
  7 purchase totals = $784.99       $860.7772   $860.77   $860.75   $860.80