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 $213.74   7.463%   $229.6914   $229.69   $229.70   $229.70  
  Purchase #2 $201.80   5.803%   $213.5105   $213.51   $213.50   $213.50  
  Purchase #3 $250.28   11.688%   $279.5327   $279.53   $279.55   $279.50  
  Purchase #4 $90.77   6.847%   $96.985   $96.99   $97.00   $97.00  
  Purchase #5 $39.57   3.111%   $40.801   $40.80   $40.80   $40.80  
  Purchase #6 $237.90   13.103%   $269.072   $269.07   $269.05   $269.10  
  Purchase #7 $93.43   13.671%   $106.2028   $106.20   $106.20   $106.20  
  7 purchase totals = $1,127.49       $1,235.7954   $1,235.79   $1,235.80   $1,235.80