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 $66.36   6.776%   $70.8566   $70.86   $70.85   $70.90  
  Purchase #2 $146.82   6.759%   $156.7436   $156.74   $156.75   $156.70  
  Purchase #3 $248.72   3.702%   $257.9276   $257.93   $257.95   $257.90  
  Purchase #4 $36.27   3.554%   $37.559   $37.56   $37.55   $37.60  
  Purchase #5 $213.90   8.396%   $231.859   $231.86   $231.85   $231.90  
  Purchase #6 $223.30   11.645%   $249.3033   $249.30   $249.30   $249.30  
  Purchase #7 $62.69   8.511%   $68.0255   $68.03   $68.05   $68.00  
  7 purchase totals = $998.06       $1,072.2746   $1,072.28   $1,072.30   $1,072.30