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 $175.59   12.722%   $197.9286   $197.93   $197.95   $197.90  
  Purchase #2 $13.83   7.873%   $14.9188   $14.92   $14.90   $14.90  
  Purchase #3 $204.95   13.695%   $233.0179   $233.02   $233.00   $233.00  
  Purchase #4 $53.74   11.212%   $59.7653   $59.77   $59.75   $59.80  
  Purchase #5 $14.30   8.859%   $15.5668   $15.57   $15.55   $15.60  
  Purchase #6 $176.80   4.559%   $184.8603   $184.86   $184.85   $184.90  
  Purchase #7 $220.75   6.660%   $235.452   $235.45   $235.45   $235.50  
  7 purchase totals = $859.96       $941.5097   $941.52   $941.45   $941.60