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 $244.41   9.114%   $266.6855   $266.69   $266.70   $266.70  
  Purchase #2 $162.86   9.561%   $178.431   $178.43   $178.45   $178.40  
  Purchase #3 $145.55   8.508%   $157.9334   $157.93   $157.95   $157.90  
  Purchase #4 $188.36   7.770%   $202.9956   $203.00   $203.00   $203.00  
  Purchase #5 $230.52   6.140%   $244.6739   $244.67   $244.65   $244.70  
  Purchase #6 $59.99   10.848%   $66.4977   $66.50   $66.50   $66.50  
  Purchase #7 $166.83   5.111%   $175.3567   $175.36   $175.35   $175.40  
  7 purchase totals = $1,198.52       $1,292.5738   $1,292.58   $1,292.60   $1,292.60