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 $88.92   11.536%   $99.1778   $99.18   $99.20   $99.20  
  Purchase #2 $224.57   11.627%   $250.6808   $250.68   $250.70   $250.70  
  Purchase #3 $216.67   8.422%   $234.9179   $234.92   $234.90   $234.90  
  Purchase #4 $54.73   5.575%   $57.7812   $57.78   $57.80   $57.80  
  Purchase #5 $172.74   13.393%   $195.8751   $195.88   $195.90   $195.90  
  Purchase #6 $219.29   5.518%   $231.3904   $231.39   $231.40   $231.40  
  Purchase #7 $202.81   11.137%   $225.3969   $225.40   $225.40   $225.40  
  7 purchase totals = $1,179.73       $1,295.2201   $1,295.23   $1,295.30   $1,295.30