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 $198.87   6.182%   $211.1641   $211.16   $211.15   $211.20  
  Purchase #2 $54.96   8.307%   $59.5255   $59.53   $59.55   $59.50  
  Purchase #3 $37.91   10.233%   $41.7893   $41.79   $41.80   $41.80  
  Purchase #4 $206.33   12.833%   $232.8083   $232.81   $232.80   $232.80  
  Purchase #5 $83.89   9.216%   $91.6213   $91.62   $91.60   $91.60  
  Purchase #6 $133.51   6.524%   $142.2202   $142.22   $142.20   $142.20  
  Purchase #7 $119.62   5.367%   $126.04   $126.04   $126.05   $126.00  
  7 purchase totals = $835.09       $905.1687   $905.17   $905.15   $905.10