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 $106.85   10.452%   $118.018   $118.02   $118.00   $118.00  
  Purchase #2 $67.75   10.232%   $74.6822   $74.68   $74.70   $74.70  
  Purchase #3 $71.60   11.661%   $79.9493   $79.95   $79.95   $79.90  
  Purchase #4 $175.81   6.585%   $187.3871   $187.39   $187.40   $187.40  
  Purchase #5 $187.25   10.851%   $207.5685   $207.57   $207.55   $207.60  
  Purchase #6 $237.59   8.408%   $257.5666   $257.57   $257.55   $257.60  
  Purchase #7 $151.68   3.764%   $157.3892   $157.39   $157.40   $157.40  
  7 purchase totals = $998.53       $1,082.5609   $1,082.57   $1,082.55   $1,082.60