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 $41.27   8.209%   $44.6579   $44.66   $44.65   $44.70  
  Purchase #2 $128.83   9.489%   $141.0547   $141.05   $141.05   $141.10  
  Purchase #3 $197.47   8.301%   $213.862   $213.86   $213.85   $213.90  
  Purchase #4 $172.29   6.525%   $183.5319   $183.53   $183.55   $183.50  
  Purchase #5 $219.43   6.374%   $233.4165   $233.42   $233.40   $233.40  
  Purchase #6 $12.69   13.472%   $14.3996   $14.40   $14.40   $14.40  
  Purchase #7 $5.60   4.517%   $5.853   $5.85   $5.85   $5.90  
  7 purchase totals = $777.58       $836.7756   $836.77   $836.75   $836.90