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 $85.67   12.722%   $96.5689   $96.57   $96.55   $96.60  
  Purchase #2 $68.94   11.742%   $77.0349   $77.03   $77.05   $77.00  
  Purchase #3 $48.87   4.307%   $50.9748   $50.97   $50.95   $51.00  
  Purchase #4 $167.29   9.640%   $183.4168   $183.42   $183.40   $183.40  
  Purchase #5 $122.84   8.667%   $133.4865   $133.49   $133.50   $133.50  
  Purchase #6 $58.33   5.313%   $61.4291   $61.43   $61.45   $61.40  
  Purchase #7 $202.85   5.693%   $214.3983   $214.40   $214.40   $214.40  
  7 purchase totals = $754.79       $817.3093   $817.31   $817.30   $817.30