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 $98.44   3.643%   $102.0262   $102.03   $102.05   $102.00  
  Purchase #2 $244.62   5.434%   $257.9127   $257.91   $257.90   $257.90  
  Purchase #3 $209.73   6.580%   $223.5302   $223.53   $223.55   $223.50  
  Purchase #4 $230.99   5.400%   $243.4635   $243.46   $243.45   $243.50  
  Purchase #5 $87.61   6.803%   $93.5701   $93.57   $93.55   $93.60  
  Purchase #6 $244.30   13.454%   $277.1681   $277.17   $277.15   $277.20  
  Purchase #7 $240.48   10.646%   $266.0815   $266.08   $266.10   $266.10  
  7 purchase totals = $1,356.17       $1,463.7523   $1,463.75   $1,463.75   $1,463.80