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 $160.85   7.665%   $173.1792   $173.18   $173.20   $173.20  
  Purchase #2 $215.93   11.330%   $240.3949   $240.39   $240.40   $240.40  
  Purchase #3 $203.45   7.514%   $218.7372   $218.74   $218.75   $218.70  
  Purchase #4 $174.51   11.643%   $194.8282   $194.83   $194.85   $194.80  
  Purchase #5 $207.82   8.119%   $224.6929   $224.69   $224.70   $224.70  
  Purchase #6 $195.72   12.779%   $220.7311   $220.73   $220.75   $220.70  
  Purchase #7 $164.69   8.651%   $178.9373   $178.94   $178.95   $178.90  
  7 purchase totals = $1,322.97       $1,451.5008   $1,451.50   $1,451.60   $1,451.40