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 $244.58   12.241%   $274.519   $274.52   $274.50   $274.50  
  Purchase #2 $151.42   4.114%   $157.6494   $157.65   $157.65   $157.60  
  Purchase #3 $23.85   10.135%   $26.2672   $26.27   $26.25   $26.30  
  Purchase #4 $224.37   4.218%   $233.8339   $233.83   $233.85   $233.80  
  Purchase #5 $169.53   11.829%   $189.5837   $189.58   $189.60   $189.60  
  Purchase #6 $153.31   9.171%   $167.3701   $167.37   $167.35   $167.40  
  Purchase #7 $8.40   7.296%   $9.0129   $9.01   $9.00   $9.00  
  7 purchase totals = $975.46       $1,058.2362   $1,058.23   $1,058.20   $1,058.20