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 $151.65   10.473%   $167.5323   $167.53   $167.55   $167.50  
  Purchase #2 $222.81   9.136%   $243.1659   $243.17   $243.15   $243.20  
  Purchase #3 $168.84   3.538%   $174.8136   $174.81   $174.80   $174.80  
  Purchase #4 $24.91   6.840%   $26.6138   $26.61   $26.60   $26.60  
  Purchase #5 $130.75   13.171%   $147.9711   $147.97   $147.95   $148.00  
  Purchase #6 $69.50   12.802%   $78.3974   $78.40   $78.40   $78.40  
  Purchase #7 $31.91   8.655%   $34.6718   $34.67   $34.65   $34.70  
  7 purchase totals = $800.37       $873.1659   $873.16   $873.10   $873.20