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 $70.87   5.803%   $74.9826   $74.98   $75.00   $75.00  
  Purchase #2 $118.87   5.527%   $125.4399   $125.44   $125.45   $125.40  
  Purchase #3 $40.54   9.193%   $44.2668   $44.27   $44.25   $44.30  
  Purchase #4 $207.71   3.728%   $215.4534   $215.45   $215.45   $215.50  
  Purchase #5 $189.30   9.229%   $206.7705   $206.77   $206.75   $206.80  
  Purchase #6 $190.49   4.212%   $198.5134   $198.51   $198.50   $198.50  
  Purchase #7 $197.74   4.217%   $206.0787   $206.08   $206.10   $206.10  
  7 purchase totals = $1,015.52       $1,071.5053   $1,071.50   $1,071.50   $1,071.60