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 $234.52   3.122%   $241.8417   $241.84   $241.85   $241.80  
  Purchase #2 $60.41   8.823%   $65.74   $65.74   $65.75   $65.70  
  Purchase #3 $74.85   9.173%   $81.716   $81.72   $81.70   $81.70  
  Purchase #4 $169.91   3.613%   $176.0488   $176.05   $176.05   $176.00  
  Purchase #5 $21.83   11.334%   $24.3042   $24.30   $24.30   $24.30  
  Purchase #6 $194.88   9.449%   $213.2942   $213.29   $213.30   $213.30  
  Purchase #7 $186.61   8.227%   $201.9624   $201.96   $201.95   $202.00  
  7 purchase totals = $943.01       $1,004.9073   $1,004.90   $1,004.90   $1,004.80