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 $62.69   12.245%   $70.3664   $70.37   $70.35   $70.40  
  Purchase #2 $245.42   6.745%   $261.9736   $261.97   $261.95   $262.00  
  Purchase #3 $184.94   11.307%   $205.8512   $205.85   $205.85   $205.90  
  Purchase #4 $45.76   11.449%   $50.9991   $51.00   $51.00   $51.00  
  Purchase #5 $172.55   8.350%   $186.9579   $186.96   $186.95   $187.00  
  Purchase #6 $186.69   8.298%   $202.1815   $202.18   $202.20   $202.20  
  Purchase #7 $169.84   13.115%   $192.1145   $192.11   $192.10   $192.10  
  7 purchase totals = $1,067.89       $1,170.4442   $1,170.44   $1,170.40   $1,170.60