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 $191.46   7.161%   $205.1705   $205.17   $205.15   $205.20  
  Purchase #2 $101.44   13.737%   $115.3748   $115.37   $115.35   $115.40  
  Purchase #3 $147.95   13.443%   $167.8389   $167.84   $167.85   $167.80  
  Purchase #4 $14.37   11.707%   $16.0523   $16.05   $16.05   $16.10  
  Purchase #5 $163.97   5.678%   $173.2802   $173.28   $173.30   $173.30  
  Purchase #6 $230.69   12.554%   $259.6508   $259.65   $259.65   $259.70  
  Purchase #7 $128.36   6.168%   $136.2772   $136.28   $136.30   $136.30  
  7 purchase totals = $978.24       $1,073.6447   $1,073.64   $1,073.65   $1,073.80