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 $83.89   11.608%   $93.628   $93.63   $93.65   $93.60  
  Purchase #2 $226.55   12.172%   $254.1257   $254.13   $254.15   $254.10  
  Purchase #3 $165.67   6.242%   $176.0111   $176.01   $176.00   $176.00  
  Purchase #4 $121.81   8.648%   $132.3441   $132.34   $132.35   $132.30  
  Purchase #5 $87.49   4.854%   $91.7368   $91.74   $91.75   $91.70  
  Purchase #6 $119.58   7.212%   $128.2041   $128.20   $128.20   $128.20  
  Purchase #7 $191.69   9.508%   $209.9159   $209.92   $209.90   $209.90  
  7 purchase totals = $996.68       $1,085.9657   $1,085.97   $1,086.00   $1,085.80