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 $70.52   3.603%   $73.0608   $73.06   $73.05   $73.10  
  Purchase #2 $153.66   5.191%   $161.6365   $161.64   $161.65   $161.60  
  Purchase #3 $128.45   11.666%   $143.435   $143.44   $143.45   $143.40  
  Purchase #4 $190.73   3.273%   $196.9726   $196.97   $196.95   $197.00  
  Purchase #5 $124.66   5.247%   $131.2009   $131.20   $131.20   $131.20  
  Purchase #6 $177.26   13.494%   $201.1795   $201.18   $201.20   $201.20  
  Purchase #7 $48.89   13.683%   $55.5796   $55.58   $55.60   $55.60  
  7 purchase totals = $894.17       $963.0649   $963.07   $963.10   $963.10