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 $160.75   5.479%   $169.5575   $169.56   $169.55   $169.60  
  Purchase #2 $237.37   13.469%   $269.3414   $269.34   $269.35   $269.30  
  Purchase #3 $136.88   12.412%   $153.8695   $153.87   $153.85   $153.90  
  Purchase #4 $112.92   11.625%   $126.047   $126.05   $126.05   $126.00  
  Purchase #5 $65.82   7.544%   $70.7855   $70.79   $70.80   $70.80  
  Purchase #6 $184.69   10.836%   $204.703   $204.70   $204.70   $204.70  
  Purchase #7 $221.35   8.685%   $240.5742   $240.57   $240.55   $240.60  
  7 purchase totals = $1,119.78       $1,234.8781   $1,234.88   $1,234.85   $1,234.90