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 $104.80   13.861%   $119.3263   $119.33   $119.35   $119.30  
  Purchase #2 $18.34   3.129%   $18.9139   $18.91   $18.90   $18.90  
  Purchase #3 $249.34   4.442%   $260.4157   $260.42   $260.40   $260.40  
  Purchase #4 $206.52   12.104%   $231.5172   $231.52   $231.50   $231.50  
  Purchase #5 $153.86   6.643%   $164.0809   $164.08   $164.10   $164.10  
  Purchase #6 $125.87   10.190%   $138.6962   $138.70   $138.70   $138.70  
  Purchase #7 $167.65   10.657%   $185.5165   $185.52   $185.50   $185.50  
  7 purchase totals = $1,026.38       $1,118.4667   $1,118.48   $1,118.45   $1,118.40