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 $241.84   10.133%   $266.3456   $266.35   $266.35   $266.30  
  Purchase #2 $95.66   8.176%   $103.4812   $103.48   $103.50   $103.50  
  Purchase #3 $65.33   8.134%   $70.6439   $70.64   $70.65   $70.60  
  Purchase #4 $204.93   3.793%   $212.703   $212.70   $212.70   $212.70  
  Purchase #5 $169.93   7.819%   $183.2168   $183.22   $183.20   $183.20  
  Purchase #6 $139.46   3.172%   $143.8837   $143.88   $143.90   $143.90  
  Purchase #7 $23.74   10.377%   $26.2035   $26.20   $26.20   $26.20  
  7 purchase totals = $940.89       $1,006.4777   $1,006.47   $1,006.50   $1,006.40