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 $62.65   10.631%   $69.3103   $69.31   $69.30   $69.30  
  Purchase #2 $225.48   3.654%   $233.719   $233.72   $233.70   $233.70  
  Purchase #3 $70.54   5.674%   $74.5424   $74.54   $74.55   $74.50  
  Purchase #4 $61.71   7.314%   $66.2235   $66.22   $66.20   $66.20  
  Purchase #5 $188.94   3.605%   $195.7513   $195.75   $195.75   $195.80  
  Purchase #6 $177.97   5.317%   $187.4327   $187.43   $187.45   $187.40  
  Purchase #7 $87.67   7.874%   $94.5731   $94.57   $94.55   $94.60  
  7 purchase totals = $874.96       $921.5523   $921.54   $921.50   $921.50