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 $195.86   3.163%   $202.0551   $202.06   $202.05   $202.10  
  Purchase #2 $236.35   6.179%   $250.9541   $250.95   $250.95   $251.00  
  Purchase #3 $186.36   13.564%   $211.6379   $211.64   $211.65   $211.60  
  Purchase #4 $203.87   3.671%   $211.3541   $211.35   $211.35   $211.40  
  Purchase #5 $140.63   7.518%   $151.2026   $151.20   $151.20   $151.20  
  Purchase #6 $167.96   8.349%   $181.983   $181.98   $182.00   $182.00  
  Purchase #7 $144.79   12.498%   $162.8859   $162.89   $162.90   $162.90  
  7 purchase totals = $1,275.82       $1,372.0727   $1,372.07   $1,372.10   $1,372.20