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 $30.66   10.133%   $33.7668   $33.77   $33.75   $33.80  
  Purchase #2 $29.37   3.294%   $30.3374   $30.34   $30.35   $30.30  
  Purchase #3 $97.41   3.446%   $100.7667   $100.77   $100.75   $100.80  
  Purchase #4 $247.64   3.821%   $257.1023   $257.10   $257.10   $257.10  
  Purchase #5 $218.29   11.729%   $243.8932   $243.89   $243.90   $243.90  
  Purchase #6 $198.36   3.859%   $206.0147   $206.01   $206.00   $206.00  
  Purchase #7 $131.31   5.747%   $138.8564   $138.86   $138.85   $138.90  
  7 purchase totals = $953.04       $1,010.7375   $1,010.74   $1,010.70   $1,010.80