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 $240.84   10.549%   $266.2462   $266.25   $266.25   $266.20  
  Purchase #2 $14.88   5.561%   $15.7075   $15.71   $15.70   $15.70  
  Purchase #3 $191.85   11.483%   $213.8801   $213.88   $213.90   $213.90  
  Purchase #4 $181.52   10.400%   $200.3981   $200.40   $200.40   $200.40  
  Purchase #5 $202.33   5.109%   $212.667   $212.67   $212.65   $212.70  
  Purchase #6 $188.27   8.551%   $204.369   $204.37   $204.35   $204.40  
  Purchase #7 $161.94   4.508%   $169.2403   $169.24   $169.25   $169.20  
  7 purchase totals = $1,181.63       $1,282.5082   $1,282.52   $1,282.50   $1,282.50