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 $212.58   7.276%   $228.0473   $228.05   $228.05   $228.00  
  Purchase #2 $161.28   6.374%   $171.56   $171.56   $171.55   $171.60  
  Purchase #3 $38.62   11.507%   $43.064   $43.06   $43.05   $43.10  
  Purchase #4 $168.87   11.239%   $187.8493   $187.85   $187.85   $187.80  
  Purchase #5 $26.30   10.260%   $28.9984   $29.00   $29.00   $29.00  
  Purchase #6 $92.29   11.799%   $103.1793   $103.18   $103.20   $103.20  
  Purchase #7 $10.69   10.684%   $11.8321   $11.83   $11.85   $11.80  
  7 purchase totals = $710.63       $774.5304   $774.53   $774.55   $774.50