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 $68.59   8.157%   $74.1849   $74.18   $74.20   $74.20  
  Purchase #2 $56.29   7.868%   $60.7189   $60.72   $60.70   $60.70  
  Purchase #3 $122.80   6.308%   $130.5462   $130.55   $130.55   $130.50  
  Purchase #4 $115.42   8.734%   $125.5008   $125.50   $125.50   $125.50  
  Purchase #5 $11.39   7.396%   $12.2324   $12.23   $12.25   $12.20  
  Purchase #6 $115.86   11.740%   $129.462   $129.46   $129.45   $129.50  
  Purchase #7 $222.47   8.560%   $241.5134   $241.51   $241.50   $241.50  
  7 purchase totals = $712.82       $774.1586   $774.15   $774.15   $774.10