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 $188.40   10.220%   $207.6545   $207.65   $207.65   $207.70  
  Purchase #2 $163.43   11.136%   $181.6296   $181.63   $181.65   $181.60  
  Purchase #3 $6.37   10.595%   $7.0449   $7.04   $7.05   $7.00  
  Purchase #4 $118.31   7.428%   $127.0981   $127.10   $127.10   $127.10  
  Purchase #5 $31.51   12.315%   $35.3905   $35.39   $35.40   $35.40  
  Purchase #6 $184.65   11.406%   $205.7112   $205.71   $205.70   $205.70  
  Purchase #7 $247.54   5.810%   $261.9221   $261.92   $261.90   $261.90  
  7 purchase totals = $940.21       $1,026.4509   $1,026.44   $1,026.45   $1,026.40