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 $153.53   6.507%   $163.5202   $163.52   $163.50   $163.50  
  Purchase #2 $204.60   9.818%   $224.6876   $224.69   $224.70   $224.70  
  Purchase #3 $233.44   5.304%   $245.8217   $245.82   $245.80   $245.80  
  Purchase #4 $231.25   11.298%   $257.3766   $257.38   $257.40   $257.40  
  Purchase #5 $79.72   8.803%   $86.7378   $86.74   $86.75   $86.70  
  Purchase #6 $195.56   9.257%   $213.663   $213.66   $213.65   $213.70  
  Purchase #7 $210.79   6.665%   $224.8392   $224.84   $224.85   $224.80  
  7 purchase totals = $1,308.89       $1,416.6461   $1,416.65   $1,416.65   $1,416.60