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 $187.62   13.314%   $212.5997   $212.60   $212.60   $212.60  
  Purchase #2 $24.39   7.703%   $26.2688   $26.27   $26.25   $26.30  
  Purchase #3 $230.84   4.423%   $241.0501   $241.05   $241.05   $241.10  
  Purchase #4 $71.66   5.507%   $75.6063   $75.61   $75.60   $75.60  
  Purchase #5 $65.58   13.349%   $74.3343   $74.33   $74.35   $74.30  
  Purchase #6 $158.50   11.313%   $176.4311   $176.43   $176.45   $176.40  
  Purchase #7 $169.96   4.151%   $177.015   $177.02   $177.00   $177.00  
  7 purchase totals = $908.55       $983.3053   $983.31   $983.30   $983.30