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 $210.82   6.109%   $223.699   $223.70   $223.70   $223.70  
  Purchase #2 $105.91   10.807%   $117.3557   $117.36   $117.35   $117.40  
  Purchase #3 $161.70   9.192%   $176.5635   $176.56   $176.55   $176.60  
  Purchase #4 $69.85   9.158%   $76.2469   $76.25   $76.25   $76.20  
  Purchase #5 $80.84   5.244%   $85.0792   $85.08   $85.10   $85.10  
  Purchase #6 $241.97   8.334%   $262.1358   $262.14   $262.15   $262.10  
  Purchase #7 $56.40   7.364%   $60.5533   $60.55   $60.55   $60.60  
  7 purchase totals = $927.49       $1,001.6334   $1,001.64   $1,001.65   $1,001.70