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 $174.28   6.446%   $185.5141   $185.51   $185.50   $185.50  
  Purchase #2 $64.58   7.846%   $69.6469   $69.65   $69.65   $69.60  
  Purchase #3 $185.42   7.435%   $199.206   $199.21   $199.20   $199.20  
  Purchase #4 $216.93   5.473%   $228.8026   $228.80   $228.80   $228.80  
  Purchase #5 $87.85   6.612%   $93.6586   $93.66   $93.65   $93.70  
  Purchase #6 $200.36   8.709%   $217.8094   $217.81   $217.80   $217.80  
  Purchase #7 $169.26   3.389%   $174.9962   $175.00   $175.00   $175.00  
  7 purchase totals = $1,098.68       $1,169.6338   $1,169.64   $1,169.60   $1,169.60