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 $203.94   6.548%   $217.294   $217.29   $217.30   $217.30  
  Purchase #2 $49.36   6.709%   $52.6716   $52.67   $52.65   $52.70  
  Purchase #3 $250.88   7.500%   $269.696   $269.70   $269.70   $269.70  
  Purchase #4 $84.79   7.421%   $91.0823   $91.08   $91.10   $91.10  
  Purchase #5 $187.47   5.685%   $198.1277   $198.13   $198.15   $198.10  
  Purchase #6 $82.32   12.123%   $92.2997   $92.30   $92.30   $92.30  
  Purchase #7 $84.66   12.416%   $95.1714   $95.17   $95.15   $95.20  
  7 purchase totals = $943.42       $1,016.3427   $1,016.34   $1,016.35   $1,016.40