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 $145.84   13.111%   $164.9611   $164.96   $164.95   $165.00  
  Purchase #2 $145.58   5.686%   $153.8577   $153.86   $153.85   $153.90  
  Purchase #3 $62.94   11.519%   $70.1901   $70.19   $70.20   $70.20  
  Purchase #4 $118.40   3.386%   $122.409   $122.41   $122.40   $122.40  
  Purchase #5 $226.75   6.629%   $241.7813   $241.78   $241.80   $241.80  
  Purchase #6 $156.91   12.414%   $176.3888   $176.39   $176.40   $176.40  
  Purchase #7 $192.88   10.547%   $213.2231   $213.22   $213.20   $213.20  
  7 purchase totals = $1,049.30       $1,142.8111   $1,142.81   $1,142.80   $1,142.90