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 $87.39   12.206%   $98.0568   $98.06   $98.05   $98.10  
  Purchase #2 $93.69   11.372%   $104.3444   $104.34   $104.35   $104.30  
  Purchase #3 $91.99   12.185%   $103.199   $103.20   $103.20   $103.20  
  Purchase #4 $60.77   6.433%   $64.6793   $64.68   $64.70   $64.70  
  Purchase #5 $10.47   10.268%   $11.5451   $11.55   $11.55   $11.50  
  Purchase #6 $181.70   7.614%   $195.5346   $195.53   $195.55   $195.50  
  Purchase #7 $138.35   4.112%   $144.039   $144.04   $144.05   $144.00  
  7 purchase totals = $664.36       $721.3982   $721.40   $721.45   $721.30