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 $90.91   12.351%   $102.1383   $102.14   $102.15   $102.10  
  Purchase #2 $237.56   5.416%   $250.4262   $250.43   $250.45   $250.40  
  Purchase #3 $151.49   13.447%   $171.8609   $171.86   $171.85   $171.90  
  Purchase #4 $130.42   9.222%   $142.4473   $142.45   $142.45   $142.40  
  Purchase #5 $118.27   7.390%   $127.0102   $127.01   $127.00   $127.00  
  Purchase #6 $153.26   8.818%   $166.7745   $166.77   $166.75   $166.80  
  Purchase #7 $195.92   5.395%   $206.4899   $206.49   $206.50   $206.50  
  7 purchase totals = $1,077.83       $1,167.1473   $1,167.15   $1,167.15   $1,167.10