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 $61.46   8.458%   $66.6583   $66.66   $66.65   $66.70  
  Purchase #2 $152.45   7.559%   $163.9737   $163.97   $163.95   $164.00  
  Purchase #3 $45.37   11.355%   $50.5218   $50.52   $50.50   $50.50  
  Purchase #4 $68.32   5.431%   $72.0305   $72.03   $72.05   $72.00  
  Purchase #5 $201.62   6.528%   $214.7818   $214.78   $214.80   $214.80  
  Purchase #6 $133.42   6.104%   $141.564   $141.56   $141.55   $141.60  
  Purchase #7 $80.72   7.869%   $87.0719   $87.07   $87.05   $87.10  
  7 purchase totals = $743.36       $796.6020   $796.59   $796.55   $796.70