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 $105.93   11.524%   $118.1374   $118.14   $118.15   $118.10  
  Purchase #2 $244.61   5.108%   $257.1047   $257.10   $257.10   $257.10  
  Purchase #3 $187.95   8.106%   $203.1852   $203.19   $203.20   $203.20  
  Purchase #4 $191.55   6.745%   $204.47   $204.47   $204.45   $204.50  
  Purchase #5 $143.90   11.499%   $160.4471   $160.45   $160.45   $160.40  
  Purchase #6 $169.43   8.779%   $184.3043   $184.30   $184.30   $184.30  
  Purchase #7 $222.85   11.682%   $248.8833   $248.88   $248.90   $248.90  
  7 purchase totals = $1,266.22       $1,376.5320   $1,376.53   $1,376.55   $1,376.50