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 $109.67   5.777%   $116.0056   $116.01   $116.00   $116.00  
  Purchase #2 $196.25   13.783%   $223.2991   $223.30   $223.30   $223.30  
  Purchase #3 $174.33   10.148%   $192.021   $192.02   $192.00   $192.00  
  Purchase #4 $247.26   4.189%   $257.6177   $257.62   $257.60   $257.60  
  Purchase #5 $170.84   8.810%   $185.891   $185.89   $185.90   $185.90  
  Purchase #6 $153.92   8.380%   $166.8185   $166.82   $166.80   $166.80  
  Purchase #7 $170.46   13.751%   $193.9   $193.90   $193.90   $193.90  
  7 purchase totals = $1,222.73       $1,335.5529   $1,335.56   $1,335.50   $1,335.50