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 $238.51   12.218%   $267.6512   $267.65   $267.65   $267.70  
  Purchase #2 $187.47   4.631%   $196.1517   $196.15   $196.15   $196.20  
  Purchase #3 $103.38   4.387%   $107.9153   $107.92   $107.90   $107.90  
  Purchase #4 $54.93   5.770%   $58.0995   $58.10   $58.10   $58.10  
  Purchase #5 $217.70   5.809%   $230.3462   $230.35   $230.35   $230.30  
  Purchase #6 $185.48   8.821%   $201.8412   $201.84   $201.85   $201.80  
  Purchase #7 $214.29   10.727%   $237.2769   $237.28   $237.30   $237.30  
  7 purchase totals = $1,201.76       $1,299.2820   $1,299.29   $1,299.30   $1,299.30