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 $63.53   7.143%   $68.0679   $68.07   $68.05   $68.10  
  Purchase #2 $118.47   8.581%   $128.6359   $128.64   $128.65   $128.60  
  Purchase #3 $189.86   4.441%   $198.2917   $198.29   $198.30   $198.30  
  Purchase #4 $87.26   11.465%   $97.2644   $97.26   $97.25   $97.30  
  Purchase #5 $243.71   10.668%   $269.709   $269.71   $269.70   $269.70  
  Purchase #6 $247.73   10.667%   $274.1554   $274.16   $274.15   $274.20  
  Purchase #7 $171.45   7.359%   $184.067   $184.07   $184.05   $184.10  
  7 purchase totals = $1,122.01       $1,220.1913   $1,220.20   $1,220.15   $1,220.30