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 $233.70   7.709%   $251.7159   $251.72   $251.70   $251.70  
  Purchase #2 $171.41   13.735%   $194.9532   $194.95   $194.95   $195.00  
  Purchase #3 $33.56   3.234%   $34.6453   $34.65   $34.65   $34.60  
  Purchase #4 $238.66   12.226%   $267.8386   $267.84   $267.85   $267.80  
  Purchase #5 $192.36   8.807%   $209.3011   $209.30   $209.30   $209.30  
  Purchase #6 $186.88   10.228%   $205.9941   $205.99   $206.00   $206.00  
  Purchase #7 $7.80   5.423%   $8.223   $8.22   $8.20   $8.20  
  7 purchase totals = $1,064.37       $1,172.6712   $1,172.67   $1,172.65   $1,172.60