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 $168.51   10.836%   $186.7697   $186.77   $186.75   $186.80  
  Purchase #2 $22.99   10.734%   $25.4577   $25.46   $25.45   $25.50  
  Purchase #3 $106.49   11.453%   $118.6863   $118.69   $118.70   $118.70  
  Purchase #4 $174.46   9.856%   $191.6548   $191.65   $191.65   $191.70  
  Purchase #5 $85.40   13.524%   $96.9495   $96.95   $96.95   $96.90  
  Purchase #6 $41.65   9.636%   $45.6634   $45.66   $45.65   $45.70  
  Purchase #7 $173.60   4.112%   $180.7384   $180.74   $180.75   $180.70  
  7 purchase totals = $773.10       $845.9198   $845.92   $845.90   $846.00