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 $157.51   5.371%   $165.9699   $165.97   $165.95   $166.00  
  Purchase #2 $185.89   11.597%   $207.4477   $207.45   $207.45   $207.40  
  Purchase #3 $153.38   7.434%   $164.7823   $164.78   $164.80   $164.80  
  Purchase #4 $145.48   5.615%   $153.6487   $153.65   $153.65   $153.60  
  Purchase #5 $192.96   13.822%   $219.6309   $219.63   $219.65   $219.60  
  Purchase #6 $182.53   4.870%   $191.4192   $191.42   $191.40   $191.40  
  Purchase #7 $122.48   5.559%   $129.2887   $129.29   $129.30   $129.30  
  7 purchase totals = $1,140.23       $1,232.1874   $1,232.19   $1,232.20   $1,232.10