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 $31.82   8.619%   $34.5626   $34.56   $34.55   $34.60  
  Purchase #2 $154.51   8.521%   $167.6758   $167.68   $167.70   $167.70  
  Purchase #3 $189.64   8.560%   $205.8732   $205.87   $205.85   $205.90  
  Purchase #4 $160.36   7.509%   $172.4014   $172.40   $172.40   $172.40  
  Purchase #5 $176.81   4.217%   $184.2661   $184.27   $184.25   $184.30  
  Purchase #6 $118.46   8.179%   $128.1488   $128.15   $128.15   $128.10  
  Purchase #7 $150.97   6.147%   $160.2501   $160.25   $160.25   $160.30  
  7 purchase totals = $982.57       $1,053.1780   $1,053.18   $1,053.15   $1,053.30